Method and system for exhaust particulate matter sensing

ABSTRACT

Methods and systems are provided for sensing particulate matter by a particulate matter (PM) sensor positioned downstream of a diesel particulate filter in an exhaust system. In one example, a PM sensor assembly may include rows of flow guides separated from each other by a gap where each of the flow guide includes a positive and negative electrode formed on opposite side surfaces. By aligning projections in the gap between successive flow guides, exhaust PM may be circulated in the gap between the electrodes for a longer time, thus increasing the probability of capture across the electrodes, and thereby increasing the sensitivity of the assembly to detection of exhaust PM.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 14/947,853, entitled “METHOD AND SYSTEM FOR EXHAUSTPARTICULATE MATTER SENSING,” filed on Nov. 20, 2015, the entire contentsof which are hereby incorporated by reference for all purposes.

FIELD

The present description relates generally to the design and use ofresistive-type particle matter (PM) sensors in an exhaust gas flow.

BACKGROUND/SUMMARY

Diesel combustion may generate emissions, including particulate matter(PM). The particulate matter may include diesel soot and aerosols suchas ash particulates, metallic abrasion particles, sulfates, andsilicates. When released into the atmosphere, PM can take the form ofindividual particles or chain aggregates, with most in the invisiblesub-micrometer range of 100 nanometers. Various technologies have beendeveloped for identifying and filtering out exhaust PMs before theexhaust is released to the atmosphere.

As an example, soot sensors, also known as PM sensors, may be used invehicles having internal combustion engines. A PM sensor may be locatedupstream and/or downstream of a diesel particulate filter (DPF), and maybe used to sense PM loading on the filter and diagnose operation of theDPF. Typically, the PM sensor may sense a particulate matter or sootload based on a correlation between a measured change in electricalconductivity (or resistivity) between a pair of thin electrodes placedon a planar substrate surface of the sensor with the amount of PMdeposited between the measuring electrodes. Specifically, the measuredconductivity provides a measure of soot accumulation.

An example PM sensor is shown by Goulette et. al. in US 2015/0153249 A1.Therein, a conductive material disposed on a substrate is patterned toform interdigitated “comb” electrodes of a PM sensor. When a voltage isapplied across the electrodes, soot particles are accumulated at or nearthe surface of the substrate between the electrodes.

The inventors herein have recognized potential issues with such systems.As an example, in such PM sensors, only a small fraction of the PM inthe incoming exhaust experiences the electrostatic forces exertedbetween the electrodes and gets collected across the electrodes formedon the surface of the sensor, thereby leading to low sensitivity of thesensors. Further, even the fraction of the PM that is accumulated on thesurface may not be uniform due to a bias in flow distribution across thesurface of the sensor. The non-uniform deposition of the PM on thesensor surface may further exacerbate the issue of low sensitivity ofthe sensor. The inventors have recognized the above issues andidentified an approach to at least partly address the issues. In oneexample, the issues above may be addressed by a sensor assembly,comprising rows of flow guides arranged between a front surface and arear surface of the assembly, each flow guide having a positiveelectrode and a negative electrode formed along opposite surfaces of theflow guide, a plurality of gaps formed between the flow guides, andmultiple projections arranged between a top surface and a bottom surfaceof the assembly, the multiple projections aligned between the pluralityof gaps. In this way, by aligning each projection in the gap formedbetween two adjacent flow guides, soot particles in the exhaust may bepushed further into the gap and closer to the electrodes formed acrossthe gap. Therefore, the probability of capture of the soot particles inthe gap across the electrodes is increased and thus, the sensitivity ofthe sensor assembly to capture soot particles in the exhaust passage isincreased.

As one example, an exhaust PM sensor assembly may be positioneddownstream of an exhaust particulate filter in an exhaust passage. ThePM sensor assembly may be a box-type sensor including rows of flowguides that are arranged inside the sensor assembly. Specifically thesensor assembly may include sealed bottom, top, and side surfaces, andfurther include open front, and rear surfaces, for directing exhaustinside and out of the assembly. Within the assembly, rows of flow guidesmay be arranged transversely between the front and the rear surface.Herein, the flow guides may include rectangular blocks separated by agap extending longitudinally between the side surfaces. In addition, therectangular blocks may include positive and negative electrodes formedalong two different, yet parallel side surfaces of the rectangularblocks. In one example, the rectangular blocks may be arranged such thatthe positive electrodes of all the rectangular blocks face towards thefront surface of the assembly and the negative electrodes of all therectangular blocks face towards the rear surface of the assembly. Insuch an example, soot accumulation may occur in the gap between therectangular blocks where the positive electrode of each rectangularblock faces the negative electrode of the neighboring rectangular block.Additionally, the assembly may include projections arranged between thetop surface and the bottom surface of the assembly. Herein, theprojections may be aligned with respect to the gap between the blocks.Specifically, the projections may be configured to direct the sootparticles closer into the gap and trap the particles inside the gap fora longer time, thereby allowing the soot particles to be closer to theelectrodes for a longer time. Thus, the probability of soot capture inthe gap across the electrodes is increased. In one example, triangularprism shaped projections may be included. Herein, the technical effectof including the projections is to exert a mechanical force on theincoming soot particles and push them closer to the electrodes where thesoot particles may experience a greater electrostatic force. In thisway, more of the incoming soot particulates may be captured by thesensor assembly. In another example, the projections may includetriangular shields that may be configures to circulate the sootparticulates for a longer duration in the region enclosed within thetriangular shields, specifically in the gap between the electrodes,thereby increasing the amount of particulates captured across theelectrodes in the gap. Overall, these characteristics of the sensorassembly may cause an output of the sensor assembly to be more accurate,thereby increasing the accuracy of estimating particulate loading on aparticulate filter.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine and an associatedparticulate matter (PM) sensor positioned in an exhaust flow.

FIGS. 2A-2C show magnified views of the PM sensor including protrudingelectrodes, and flow guides positioned there within.

FIG. 3 shows multiple soot bridge pathways generated at each of theblocks of the flow guides.

FIG. 4 shows a flow chart depicting a method for dividing incoming PMstreams into multiple PM streams at multiple flow guides positioned on asurface of the PM sensor.

FIG. 5 shows a flow chart depicting a method for performing regenerationof the PM sensor.

FIG. 6 shows a flow chart depicting a method for diagnosing leaks in aparticulate filter positioned upstream of the PM sensor.

FIG. 7 shows an example relationship between a soot load of the PMsensor, a total length of the soot bridges and soot load on theparticulate filter.

FIG. 8 shows an example embodiment of a PM sensor assembly withprotruding flow guides separated by a gap, and triangular projectionsaligned in the gap.

FIG. 9A shows a schematic view of the flow guides protruding from thebottom surface of the PM sensor assembly.

FIG. 9B shows a side view of the triangular projections with verticeslocated in the gap between the flow guides.

FIG. 10 shows an example embodiment of the PM sensor assembly includingflow guides suspended between a top plate and a bottom plate of theassembly and having triangular shields connecting neighboring flowguides.

FIG. 11 shows a cross-section view of the triangular shields alternatingin a direction of projection in the assembly.

FIG. 12 shows a flow chart depicting a method for directing exhaust intochannels formed between adjacent flow guides of the PM sensor assembly.

DETAILED DESCRIPTION

The following description relates to systems and methods for sensingparticulate matter (PM) in an exhaust flow of an engine system, such asthe engine system shown in FIG. 1. A PM sensor (or assembly) placed inan exhaust passage of the engine system may include a pair of protrudinginterdigitated electrodes and further include a plurality of protrudingflow guides located between alternate pairs of electrodes as shown inFIGS. 2A-2C. As such, the flow guides may include evenly spaced blocksarranged between pairs of electrodes. PM or soot entering the PM sensormay accumulate across the protruding electrodes (and not on the blocks,for example) forming PM streams or soot bridges. However, each block ofthe flow guide may block the soot bridge formation, and further dividethe soot bridge into several pathways as shown in FIG. 3. A controllermay be configured to perform a control routine, such as the routine ofFIG. 4 to divide incoming PM streams into multiple PM streams atmultiple flow guides positioned on the sensor surface. In addition, thecontroller may intermittently clean the PM sensor (as shown in themethod presented at FIG. 5) to enable continued PM detection and performdiagnostics on a particulate filter positioned upstream of the PM sensorbased on an output of the PM sensor (as shown in the method presented atFIG. 6). An example relation between a soot load of the PM sensor, atotal length of the soot bridges and soot load on the particulate filteris shown in FIG. 7. In this way, by dividing the soot bridges at eachblock, soot bridges may be formed on a larger surface area of the sensorsurface, and may further generate a uniform distribution of soot on thesensor surface. In some example embodiments, the PM sensor assembly mayinclude a box-type assembly comprising continuous rectangular blocksseparated by a gap and positioned between a front and a rear surface asshown in FIGS. 8 and 10. For example, the rectangular blocks may becoupled to a bottom plate of the sensor assembly, and a top plate mayinclude triangular projections that are aligned in the gap between theblocks as shown in FIGS. 9A, and 9B. The triangular projections mayserve to impart a mechanical force on the incoming soot particles,thereby pushing the particles closer towards the electrodes where theymay eventually accumulate. As another example, the rectangular blocksmay be suspended between the top plate and the bottom plate of theassembly as shown in FIGS. 10, and 11. In such an example, the assemblymay additionally include triangular shields connecting adjacent blocksalternately in the top and the bottom. The triangular shields may aid inthe recirculation of exhaust in the gap between the blocks, therebyincreasing a retention time of the exhaust inside the gap. Thecontroller may be configured to perform a control routine, such as theroutine of FIG. 12 to accumulate exhaust PM across the electrodes formedalong the rectangular blocks. Overall, these characteristics of thesensor may cause an output of the PM sensor to be more accurate, therebyincreasing the accuracy of estimating particulate loading on aparticulate filter. In addition, by enabling more accurate diagnosis ofthe particulate filter, exhaust emissions compliance may be improved. Assuch, this reduces the high warranty costs of replacing functionalparticulate filters and exhaust emissions are improved and exhaustcomponent life is extended.

FIG. 1 shows a schematic depiction of a vehicle system 6. The vehiclesystem 6 includes an engine system 8. The engine system 8 may include anengine 10 having a plurality of cylinders 30. Engine 10 includes anengine intake 23 and an engine exhaust 25. Engine intake 23 includes athrottle 62 fluidly coupled to the engine intake manifold 44 via anintake passage 42. The engine exhaust 25 includes an exhaust manifold 48eventually leading to an exhaust passage 35 that routes exhaust gas tothe atmosphere. Throttle 62 may be located in intake passage 42downstream of a boosting device, such as a turbocharger (not shown), andupstream of an after-cooler (not shown). When included, the after-coolermay be configured to reduce the temperature of intake air compressed bythe boosting device.

Engine exhaust 25 may include one or more emission control devices 70,which may be mounted in a close-coupled position in the exhaust. One ormore emission control devices may include a three-way catalyst, lean NOxfilter, SCR catalyst, etc. Engine exhaust 25 may also include dieselparticulate filter (DPF) 102, which temporarily filters PMs fromentering gases, positioned upstream of emission control device 70. Inone example, as depicted, DPF 102 is a diesel particulate matterretaining system. DPF 102 may have a monolith structure made of, forexample, cordierite or silicon carbide, with a plurality of channelsinside for filtering particulate matter from diesel exhaust gas.Tailpipe exhaust gas that has been filtered of PMs, following passagethrough DPF 102, may be measured in a PM sensor 106 and furtherprocessed in emission control device 70 and expelled to the atmospherevia exhaust passage 35. In the depicted example, PM sensor 106 is aresistive sensor that estimates the filtering efficiency of the DPF 102based on a change in conductivity measured across the electrodes of thePM sensor. A schematic view 200 of the PM sensor 106 is shown at FIGS.2A-2C, as described in further detail below.

The vehicle system 6 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust flowrate sensor 126 configured to measure a flow rate of exhaust gas throughthe exhaust passage 35, exhaust gas sensor (located in exhaust manifold48), temperature sensor 128, pressure sensor 129 (located downstream ofemission control device 70), and PM sensor 106. Other sensors such asadditional pressure, temperature, air/fuel ratio, exhaust flow rate andcomposition sensors may be coupled to various locations in the vehiclesystem 6. As another example, the actuators may include fuel injectors66, throttle 62, DPF valves that control filter regeneration (notshown), a motor actuator controlling PM sensor opening (e.g., controlleropening of a valve or plate in an inlet of the PM sensor), etc. As yetanother example, the actuators may include switches coupled to PMmeasurement circuitry. The control system 14 may include a controller12. The controller 12 may be configured with computer readableinstructions stored on non-transitory memory. The controller 12 receivessignals from the various sensors of FIGS. 1, 2A-2C, 3, 8, 9A-9B, 10, and11, processes the signals, and employs the various actuators of FIGS. 1,2A-2C, 3, 8, 9A-9B, 10, and 11 to adjust engine operation based on thereceived signals and instructions stored on a memory of the controller.As an example, while operating the PM sensor to accumulate sootparticulates, the controller send a control signal to an electriccircuit to apply a voltage to electrodes of a sensor element of the PMsensor assembly to trap the charged particulates onto the surface ofsensor electrodes of a sensor element. As another example, during PMsensor regeneration, the controller may send a control signal to aregeneration circuit to close a switch in the regeneration circuit for athreshold time to apply a voltage to a heating element coupled toelectrodes to heat the electrodes of the sensor element. In this way,the electrodes are heated to burn off soot particles deposited on thesurface of the electrodes. Example routines are described herein withreference to FIGS. 4-6, and 12.

Turning now to FIGS. 2A-2C, schematic views of an example embodiment ofa particulate matter (PM) sensor 202 (such as PM sensor 106 of FIG. 1)are shown. Specifically, FIG. 2A shows a magnified view of the PM sensorincluding a pair of interdigitated electrodes protruding from sensorsurface and further comprising a plurality of flow guides positionedthere within. FIG. 2B shows a magnified view of a region 250 of PMsensor 202 shown in FIG. 2A. FIG. 2C shows a side view of a portion ofthe PM sensor 202. The PM sensor 202 may be configured to measure PMmass and/or concentration in the exhaust gas, and as such, may becoupled to an exhaust passage (e.g., such as the exhaust passage 35shown in FIG. 1), upstream or downstream of a diesel particulate filter(such as DPF 102 shown in FIG. 1).

Turning now to FIG. 2A, schematic view 200 shows a resistive-type PMsensor 202 disposed inside an exhaust passage such that exhaust gasesflow from downstream of a diesel particulate filter towards the PMsensor 202 as indicated by arrows 220 (along Z-axis). The PM sensor 202may include a pair of planar continuous interdigitated electrodes 201and 203 forming a “comb” structure spaced at a distance from each other.As such, the PM sensor 202 with electrodes 201 and 203 may be positionedinside a protection tube (not shown) and may include conduits (notshown) within the tube that direct the exhaust gases towards theelectrodes as indicated by arrows 220. The electrodes 201 and 203 may betypically manufactured from metals such as platinum, gold, osmium,rhodium, iridium, ruthenium, aluminum, titanium, zirconium, and thelike, as well as, oxides, cements, alloys and combination comprising atleast one of the foregoing metals. The electrodes 201 and 203 are formedon a substrate 208 of the PM sensor 202 that is typically manufacturedfrom highly electrically insulating materials. Possible electricallyinsulating materials may include oxides such as alumina, zirconia,yttria, lanthanum oxide, silica, and combinations comprising at leastone of the foregoing, or any like material capable of inhibitingelectrical communication and providing physical protection for the pairof interdigitated electrodes. The interdigitated electrodes may furtherinclude plurality of “tines” 212 and 214, extending for a certain lengthinto the sensor substrate 208 (along the X-axis). The spacing betweenthe comb “tines” of the two electrodes may typically be in the rangefrom 10 micrometers to 100 micrometers with the linewidth of eachindividual “tine” being about the same value, although the latter is notnecessary. Herein, the pairs of tines of the interdigitated electrodesmay be positioned orthogonal to the exhaust flow (arrows 220).

As such, the PM sensor substrate 208 may include a heating element (notshown) and the PM sensor may be regenerated by heating the sensorsubstrate via the heating element to burn the accumulated soot particlesfrom the surface of PM sensor 202. In an alternate example, the heatingelement may be coupled to each of the flow guides (as described withreference to FIGS. 8-11). By intermittently regenerating the surface ofPM sensor 202, it may be returned to a condition more suitable forcollecting exhaust soot. In addition, accurate information pertaining tothe exhaust soot level may be inferred from the sensor regeneration andrelayed to the controller.

The PM sensor 202 including the interdigitated electrodes may be mountedon an exhaust tailpipe such that the sensing portion of the sensor thatincludes the interdigitated electrodes is extended inside the tailpipeto detect soot or PM in the incoming exhaust gases. The electrode 201may be connected to a positive terminal of a voltage source 216 of anelectric circuit 236 via a connecting wire 232. The electrode 203 may beconnected to a measurement device 218 a connecting wire 234, and furtherconnected to a negative terminal of the voltage source 216 of theelectric circuit 236. Thus, each pair of tines is alternately connectedto positive and negative terminal of the voltage source 216. Theconnecting wires 232 and 234, the voltage source 216 and the measurementdevice 218 are part of the electric circuit 236 and are housed outsidethe exhaust passage (as one example, <1 meter away). Further, thevoltage source 216 and the measurement device 218 of the electriccircuit 236 may be controlled by a controller, such as controller 12 ofFIG. 1, so that particulate matter collected at the PM sensor may beused for diagnosing leaks in the DPF, for example. As such, themeasurement device 218 may be any device capable of reading a resistancechange across the electrodes, such as a voltmeter. As PM or sootparticles get deposited between the electrodes, the resistance betweenthe electrode pair may start to decrease, which is indicated by adecrease in the voltage measured by the measurement device 218. Thecontroller 12 may be able to determine the resistance between theelectrodes as a function of voltage measured by the measurement device218 and infer a corresponding PM or soot load on the planar electrodesof the PM sensor 202. By monitoring the load on the PM sensor 202, theexhaust soot load downstream of the DPF may be determined, and therebyused to diagnose and monitor the health and functioning of the DPF. Insome examples, the controller 12 may adjust the voltage source to supplya certain voltage to the electrodes of the PM sensors. When switches aredisposed in the electric circuit, the controller 12 may determine theclosing and opening of the switches based on a condition of the PMsensor. For example, when the PM sensor is collecting PM, the switchesin the circuitry may be adjusted so that voltages are applied to theelectrodes of the sensor. However, when the PM sensor is regenerating,the switches connecting the electrodes to the voltage source may beopened. Further, the heating circuit may be turned ON by the controller.

As such, the electrode 203 may include a planar non-interdigitatedelectrode portion 206 and further include several tines 212 contiguouswith the electrode portion 206. Likewise, the electrode 201 may includea planar non-interdigitated electrode portion 204 and further includeseveral tines 214 contiguous with the electrode portion 204. Herein, thetines 212 and the 214 are planar and interdigitated for a certaindistance along the substrate 208 of the sensor forming a “comb”structure. The “comb” structure of the interdigitated electrodes maycover the portion of the planar substrate 208, which is exposed to theexhaust gases. Hereafter, the electrode 201 may be referred to as thepositive electrode and may further include both the non-interdigitatedelectrode portion 204 and the interdigitated portion or tines 214.Similarly, the electrode 203 may be referred to as the negativeelectrode may further include both the non-interdigitated electrodeportion 206 and the interdigitated portion or tines 212. The positiveelectrode and the negative planar interdigitated electrodes of thesensor may be spaced at a distance from one another and may protrudefrom the surface of the PM sensor, which will be explained in detailwith reference to FIG. 2B.

The interdigitated portion of the negative electrode or tines 212 (ninetines shown as non-limiting example of the tines) extending for lengthL_(n) into the sensor substrate 208, and is indicated by arrow 222, andfurther separated from the tines 214 by gap. Similarly, the tines 214(nine tines shown as non-limiting example of the tines) may extend for alength L_(p) into the sensor substrate 208, and is indicated by arrow224. Further, the PM sensor 202 includes plurality of protruding flowguides 205 located between the pair of planar interdigitated electrodes.Herein, the flow guide 205 includes evenly spaced blocks 210 arrangedbetween pairs of tines 212 and 214 of the interdigitated electrodes 201and 203. Furthermore, the blocks 210 may be staggered between alternatepairs of tines 212 and 214 of the interdigitated electrodes. A region250 of the PM sensor 202 is magnified in FIG. 2B for illustrativepurpose. Herein, the blocks may be arranged between the tines such thatthe blocks are directly contacting or touching each of the tines 212 and214. Further, the blocks as such may be separated from one another by aspace with no other components there between. The blocks may be composedof material that is insulating, and not conducting.

Turning now to FIG. 2B, a magnified view 255 of region 250 of the PMsensor 202 is shown. Herein, a portion of the substrate 208 includingportions of the tines 212 and 214 (four tines of alternating positiveand negative voltages are shown), and three blocks 210 are shown.Exhaust gas flow into the region 250 is indicated by arrows 220. Forillustrative purposes, the three pairs of positive and negative tinesformed by four tines shown in FIG. 2B are marked as pair 1, pair 2 andpair 3.

As opposed to thin electrodes interdigitating electrodes that aretypically used in PM sensors, both the positive electrode 201 and thenegative electrode 203 of the PM sensor 202 may protrude from the sensorsubstrate 208 to a certain height as indicated by arrows 238. In someexample embodiments, the height to which the positive electrodeprotrudes may be the same as the height to which the negative electrodeprotrudes from the surface of the sensor. In other examples, theprotruding height may be different for the positive and the negativeelectrodes. Herein, the tines 212 and 214 of the electrodes are shown toprotrude to a height (indicated by arrows 238) from the top surface ofthe substrate 208. The height (indicated by arrows 238) of the tines maybe much smaller than the length (L_(p) and L_(n) shown in FIG. 2A) ofthe tines, for example. Further, the tines 212 and 214 may be separatedby a distance shown by arrow 268. As described earlier, the spacingbetween the comb “tines” of the two electrodes may typically be in therange from 10 micrometers to 100 micrometers. The height of the tinesmay be much smaller than the spacing between the tines, for example.

As described earlier, the PM sensor 202 may include plurality ofprotruding flow guides 205 (as shown in FIG. 2A) located between thepair of planar interdigitated electrodes. The flow guide 205 includesevenly spaced blocks 210 arranged between pairs of tines 212 and 214 ofthe interdigitated electrodes 201 and 203 separated by a distanceindicated by arrow 230. Herein, the spacing between the blocks(indicated by arrow 230) may be lower than a separation between thepairs of tines (indicated by arrow 268). Further, when disposed betweentines of the interdigitated electrodes, the blocks 210 may touch boththe tines. Thus, a width of the block may be equal to the spacingbetween the tines of the electrodes.

Each block 210 may be of a height h (indicated by arrow 228) and length1 (indicated by arrow 226). The height h of each of the blocks may belarger than the height (indicated by arrow 238) of each of the pairs oftines of the interdigitated electrodes. In other words, the height ofthe blocks may be larger than the protrusion of the electrodes from thesurface of the sensor, for example. In magnified view 255 of the region250 of PM sensor 202, three blocks 210 are shown arranged between pairsof tines. Herein, two of the blocks 210 between pair 1 of the tines areseparated by a distance (see arrow 230). Another single block 210 ispositioned between pair 3 of the tines 212 and 214. Herein, no block ispositioned between pair 2 of the tines. Thus, the blocks are staggeredbetween alternate pairs of tines of the interdigitated electrodes.Furthermore, the block 210 positioned between pair 3 is positioned suchthat there is less than threshold overlap with the blocks positionedbetween pair 1, for example. In one example, the block 210 between pair3 of the tines is positioned in a region across pair 3, which overlapswith the spacing 214 between blocks positioned in pair 1. In such anexample, there is no overlap of the blocks positioned in pair 3 with theblocks positioned in pair 1. Thus, each alternate pair of tines includesblocks arranged with less than threshold overlap with blocks inpreceding alternating pairs of tines. Herein, pair 1 may be a precedingalternate pair to pair 3. In other examples, pair 3 may be a precedingalternate pair to pair 1. Thus, when the blocks are staggered along thePM sensor surface with such less than threshold overlap of blockspositioned along alternate pairs, there is room for the soot to grow anddistribute uniformly around the blocks, for example.

The blocks 210 are arranged such that they are equally spaced from theirnearest neighbors, for example. As such, the spacing between the blocks(indicated by arrow 230) may be smaller than a distance between thepairs of tines of the interdigitated electrodes (indicated by arrow268). Herein, the width of the block 210 may be equal to the distancebetween the tines of the interdigitated electrodes.

Soot or PM in the exhaust gas is typically charged. Due electrostaticattraction between the charged PM and the interdigitated electrodes, PMget deposited on the electrodes and form soot bridges across theinterdigitated electrodes. Two such example soot bridges 252 and 260 areshown in FIG. 2B. Herein, the tines 214 are connected to the positiveterminal and hence held at a positive potential, and the tines 212 areconnected to the negative terminal and hence held at a negativepotential. The electric field generated between the interdigitatedelectrodes, specifically between the tines 212 and 214 allow soot or PMto get deposited on the electrodes. However, since the blocks are notconnected to any voltage source, the soot does not grow on the blocks.The soot bridges may tend to avoid the blocks positioned between thepairs of tines and navigate towards the charged electrodes, for example.The soot bridge 252 begins to grow across pair 3 and continues to growacross pair 2 of the tines, and when it reaches pair 1, the soot bridge252 bifurcates to avoid growing on the block. While avoiding the block,the soot bridge 252 forms two pathways and continues to grow across pair1, for example. Similarly, soot bridge 260 begins to grow across pair 3and pair 2 of the tines, and when it reaches pair 1, the soot bridge 260bifurcates to avoid growing on the block. While avoiding the block, thesoot bridge 260 forms two pathways and continues to grow across pair 1,for example. Thus, soot bridges are formed between the pairs of tinesand around the blocks.

Turning to FIG. 2C, a side view 275 of a portion of the PM sensor 202 ofFIG. 2A is shown. Herein, equally spaced blocks 276 (such as blocks 210of FIGS. 2A-2B) may be placed across alternate pairs of positiveelectrode 280 (such as positive electrode 201 of FIG. 1) and negativeelectrode 278 (such as negative electrode 203 of FIG. 1) protruding froma substrate 282 (such as substrate 208 of FIGS. 2A-2B). In the view 275,exhaust flow direction is indicated by arrows 284. As described earlier,soot bridges accumulate across the electrodes due to electrostaticattraction. For example, soot bridge 286 includes a soot bridge pathway286A forming on the substrate 282 closer to the positive electrode 280.When the soot bridge pathway 286A encounters the block 276, the sootbridge may avoid the block 276 and continue to grow around the block276, thereby generating soot bridge pathway 286B. As such, block isneutral with no voltage applied to it. Hence, the soot bridge may notfeel any electrostatic force attracting it to or repelling it from theblock. However, the soot bridge may experience an electrostatic pullfrom the negative electrode 278 positioned beyond (to the left of theblock 276 in FIG. 2C) the block. Thus, soot bridge continues to beformed along soot bridge pathway 286B behind the block 276 and reachesthe negative electrode 278. The soot bride may not be able to climb overthe block to reach the negative electrode 278 since the height of theblock may be much larger than a length of the block, for example. Thus,the soot bridge bifurcates and grows around the block towards thenegative electrode.

Once the soot bridge forms a pathway around the block towards thenegative electrode 278, it may begin to feel an electrostatic pull froma succeeding positive electrode 280 positioned further along thesubstrate 282 at a distance from the negative electrode, for example.The soot bridge may continue to grow along pathway 286C towards the nextpositive electrode 280. The soot bridge may encounter another block 276.However, at block 276 the soot bridge pathway may bifurcate again, andsoot bridge may continue to grow in front of the block, for example,along soot bridge pathway 286D until it reaches the negative electrode278. Once at the negative electrode 278, the soot bridge continues togrow towards the next positive electrode 280 positioned at a distancefrom the negative electrode 278 along the soot bridge pathway 286E. Inthis way, multiple soot bridge pathways are formed across the electrodesof the sensor, specifically around the blocks staggered between theelectrodes.

Further, the PM sensor may further including a controller (such ascontroller 12 of FIG. 1) with computer-readable instructions stored onnon-transitory memory for dividing a single stream of PM in the exhaustflow into multiple streams of PM at each of the blocks located betweenthe pairs of tines of the interdigitated electrodes, depositing the PMmultiple streams of PM on the pairs of tines, and regenerating the PMsensor when a PM load between the pairs tines reaches a threshold PMload as explained in detail in FIGS. 3 and 4.

Thus, an example particulate matter (PM) sensor may include a pair ofplanar interdigitated electrodes spaced at a distance from each otherand protruding from a surface of the PM sensor; and a plurality ofprotruding flow guides located between the pair of planar interdigitatedelectrodes. Additionally or alternatively, the flow guides of the PMsensor may include evenly spaced blocks arranged between pairs of tinesof the interdigitated electrodes, spacing between the blocks beingsmaller than a distance between the pairs of tines of the pair of planarinterdigitated electrodes. Additionally or alternatively, the blocks maybe further staggered between alternate pairs of tines of theinterdigitated electrodes. Additionally or alternatively, each alternatepair of tines may include blocks arranged with less than thresholdoverlap with blocks in preceding alternating pairs of tines.Additionally or alternatively, a spacing between the blocks between thepairs of tines is lower than a separation between the pairs of tines ofthe interdigitated electrodes. Additionally or alternatively, wherein aheight of the blocks is larger than a height of each of the pairs oftines of the interdigitated electrodes. Additionally or alternatively,the pairs of tines of the interdigitated electrodes are positionedorthogonal to exhaust flow, and wherein each pair of tines arealternately connected to positive and negative terminal of a voltagesource. Additionally or alternatively, wherein soot in the exhaust flowdeposits between the pairs of tines of the interdigitated electrodesavoiding the blocks positioned between the pairs of tines. Additionallyor alternatively, the PM sensor may further including a controller withcomputer-readable instructions stored on non-transitory memory fordividing a single stream of PM in the exhaust flow into multiple streamsof PM at each of the blocks located between the pairs of tines of theinterdigitated electrodes, depositing the PM multiple streams of PM onthe pairs of tines, and regenerating the PM sensor when a PM loadbetween the pairs tines reaches a threshold PM load.

The growth of the soot bridges across the PM sensor surface and thesplitting of the soot bridge pathways may be analogous to balls droppinginto a Galton board with pins staggered across the board, for example.Turning now to FIG. 3, a schematic top view 300 of the PM sensor withblocks staggered between the interdigitated electrodes of the PM sensoris shown. Herein, the arrangement of the blocks between alternate pairsof tines of the interdigitated electrodes may be similar to arrangementof pins in a Galton board.

The PM sensor 302 may be an example of PM sensor 202 described withreference to FIGS. 2A-2C. As such the details of the PM sensor 302 maybe similar to the PM sensor 202 discussed earlier. Briefly, PM sensor302 may include a pair of continuous interdigitated planar electrodes304 and 306 separated by a gap formed on a sensor surface. The positiveelectrode 306 is connected to a positive terminal of a voltage source322 via connecting wire 326 and the negative electrode 304 is connectedto a measurement device 324 and a negative terminal of the voltagesource 322 via connecting wire 328. A controller such as controller 12of FIG. 1 may control the circuit 320 comprising of the voltage source322 and the measurement device 324.

The PM sensor 302 may include an inlet 310 and an outlet 312 alignedorthogonal to the direction of flow of exhaust gas (indicated by arrows318). The inlet 310 may guide exhaust gases from downstream of aparticulate filter into the PM sensor, specifically, towards the sensingportion of the PM sensor 302 including the interdigitated electrodes andmultiple flow guides. The outlet 312 may guide the exhaust gases out ofthe PM sensor 302 and into the tailpipe.

The PM sensor 302 may also include a plurality of uniformly spacedprotrusions positioned in a staggered arrangement along the sensorsurface. In one example, the protrusions may be blocks 308. Blocks 308may be arranged across the PM sensor 302, specifically across the tinesof the interdigitated electrodes and between alternate pairs ofinterdigitated electrodes. Herein, a height of each of the blocks may begreater than a height of each of the interdigitated electrodes. Inaddition, a length of each of the block may be smaller than a length ofthe each of the continuous interdigitated electrodes, specifically alength of the tines of the electrodes. Similar to the pins of the Galtonboard, the blocks 308 may be arranged in staggered order, and alongalternate pairs of tines of the interdigitated electrodes. Herein, 314and 315 indicate alternate pairs of the tines of the interdigitatedelectrodes 304 and 306. Similarly, 315 and 316 are alternate pairs, soare 316 and 317, and 317 and 319. Across the alternate pairs of thetines of interdigitated electrodes, the blocks 308 are staggered.Herein, blocks 308 placed across the pair 314 and the pair 315 may bepositioned in such a way that the blocks across the pair 314 are alignedwith the gaps formed between blocks 308 positioned across the pair 315.Similarly, blocks 308 placed across the pair 315 and the pair 316 may bepositioned in such a way that the blocks across the pair 315 are alignedwith the gaps formed between blocks 308 positioned across the pair 316.In the same way, blocks 308 placed across the pair 316 and the pair 317may be positioned in such a way that the blocks across the pair 317 arealigned with the gaps formed between blocks 308 positioned across thepair 318. Likewise, blocks 308 placed across the pair 317 and the pair319 may be positioned in such a way that the blocks across the pair 317are aligned with the gaps formed between blocks 308 positioned acrossthe pair 319. This arrangement of the blocks across alternate pairs oftines of the electrode may be similar to the arrangement of pins acrossthe Galton board, for example. The PM sensor 302 may additionally oralternatively include a set of blocks arranged closer to the inlet 310and another set of blocks arranged closer to the outlet 312 of thesensor.

Exhaust gases entering the PM sensor 302 may carry charged soot or PM.These charged soot or PM undergo electrostatic attraction towards thecharged electrodes of the PM sensor and form soot bridges as explainedearlier. Herein, a single stream of PM in the exhaust flow may bedivided into multiple streams of PM at each of the blocks locatedbetween the pairs of tines of the interdigitated electrodes. Further,the PM streams may be deposited on the pairs of tines of theinterdigitated electrodes. Further, soot or PM in the streams mayaccumulate across the pair of continuous interdigitated electrodes andnot accumulate across the blocks, for example.

An example stream 330 is shown in the top view 300. Stream 330 mayoriginate at the inlet 310 of the PM sensor 302, and get attracted tothe negative electrode positioned close to the inlet forming a stream332. Herein, the stream 332 may be formed in a space between the blocks.When the stream 332 reaches a block across the pair 314, the stream 332may split into two streams 336 and 334 to avoid growing on the block andto reach the negative electrode of the pair 314, for example. Thus, asingle stream 332 may be divided into two streams 336 and 334, therebyincreasing the surface area for the soot to adhere. Similarly, stream336 may spilt into streams 338 and 340 when encountering a block 308across the pair 315. Likewise, when stream 338 reaches a block acrossthe pair 316, the stream 338 may split into two streams 342 and 346 toavoid growing on the block and to reach the negative electrode of thepair 314. In a similar fashion, when the stream 342 reaches a blockacross the pair 317, the stream 342 may split into two streams 348 and350 to avoid growing on the block and to reach the negative electrode ofthe pair 314, for example. Finally, the streams may exit the PM sensor302 at the outlet 312 as indicated by arrows 358. As such, the streamsmay exit the PM sensor along the space between adjacent blockspositioned at the outlet of the PM sensor.

Herein, the pathway of each of the stream may be a “random walk” and asthe streams get spilt into multiple pathways, the surface area ofadsorption of the soot onto the interdigitated electrodes increases.Further, similar to the Galton board, the soot bridges formed whensplitting PM streams into multiple streams across the staggered blocksmay lead to a uniform distribution of soot across the PM sensorelectrode. In this way, by positioning blocks along the surface of theelectrodes, soot bridges may be formed uniformly across the surface ofthe electrode. Further, soot loading and soot bridge building activitybetween the positive and negative electrodes may occur in shorter timeframes. A controller, such as controller 12 of FIG. 1, may be able todetermine a soot load on the PM sensor based on a sum total of sootaccumulated across multiple pathways as explained with reference to FIG.4. When the soot load of the PM sensor reaches a threshold, then thesensor may be regenerated as shown in FIG. 5. In this way, the PM sensormay detect PM exiting the particulate filter more accurately, and hencediagnose the DPF for leaks in a more reliable fashion.

Thus, an example particular matter (PM) sensor, may include a pair ofcontinuous interdigitated electrodes formed on a sensor surfaceincluding a plurality of uniformly spaced protruding protrusionspositioned in a staggered arrangement along the sensor surface, theprotruding blocks positioned in between alternate pairs of theinterdigitated electrodes. Additionally or alternatively, theprotrusions may be blocks and a height of each of the blocks may begreater that a height of each of the interdigitated electrodes.Additionally or alternatively, a length of each of the blocks is smallerthan a length of each of the interdigitated electrodes. Additionally oralternatively, the PM sensor may include a controller withcomputer-readable instructions stored on non-transitory memory foraccumulating soot across the pair of continuous interdigitatedelectrodes and avoiding accumulating soot on the blocks, determining asoot load on the PM sensor based on a sum total of soot accumulatedacross the pair of interdigitated electrodes, and regenerating the PMsensor when the soot load is higher than a threshold.

Turning now to FIG. 4, illustrates a method 400 for dividing incoming PMstreams into multiple PM streams at multiple flow guides positioned on asurface of the PM sensor. Specifically, the method determines soot loadon the sensor based on a total length of soot bridges across themultiple PM streams. Instructions for carrying out method 400 and therest of the methods included herein may be executed by a controllerbased on instructions stored on a memory of the controller and inconjunction with signals received from sensors of the engine system,such as the sensors described above with reference to FIGS. 1, 2A-2C and3. The controller may employ engine actuators of the engine system toadjust engine operation, according to the methods described below.

At 402, method 400 includes determining engine operating conditions.Engine operating conditions determined may include, for example, enginespeed, engine temperature, various exhaust air-fuel ratios, variousexhaust temperatures, PM load on PM sensor, PM load on DPF, load on anexhaust LNT, ambient temperature, duration (or distance) elapsed since alast regeneration of PM sensor and DPF, etc.

Next, at 404, method 400 may divide incoming PM streams into multiple PMstreams. Further, diving the incoming PM streams into multiple PMstreams may include dividing the PM streams at multiple flow guidespositioned on a surface of the PM sensor at 406, wherein the multipleflow guides are positioned between the positive and the negativeelectrode of the PM sensor. Herein, the flow guides may include evenlyspaced blocks protruding from the surface of the sensor and furtherstaggered across alternate pairs of the positive and negative electrodesof the sensor. Diving the PM streams into multiple PM streams mayfurther include diving the PM streams at the evenly spaced blocks at408. As such, the blocks are staggered across alternate pairs of theinterdigitated electrodes, and further positioned such that there isless than threshold overlap of blocks with blocks in precedingalternating pairs of the electrodes. By placing the blocks in astaggered arrangement, PM stream may bifurcate whenever they encounter ablock in their path, and further divide into multiple streams to avoidthe block to find charged electrodes.

Next, at 410, the charged soot or PM in the PM streams may depositacross the electrodes forming soot bridges. Herein, depositing the sootbridges across the electrodes may further include guiding the sootbridges around the flow guides or blocks positioned across theelectrodes, and further generating multiple soot bridge pathways aroundthe flow guides at 412. Further, depositing the soot bridges may includedepositing the soot bridges across the positive and negative electrodeof the PM sensor and not on the flow guides at 414. Note that theactions of 404-414 describe actions occurring at the various locationsand are not code programmed into the controller, in contrast to 402, and416-426, for example.

Next, at 416, the method includes determining a length Li of each of thesoot bridges along each of the multiple soot bridge pathways. Asexplained earlier, the soot bridges may form across multiple pathways.Herein, the multiple pathways are generated by positioning blocks alongthe interdigitated electrodes, for example. As the soot bridges growsacross the electrodes, the length of the soot bridge may begin toincrease. The controller may determine a length of each of the sootbridge formed across the surface of the sensor. The controller maydetermine the length of the soot bridges based on a current measuredacross the measurement device, for example.

Method 400 proceeds to 418 where a total length of the soot bridges isdetermined by summing Li of all the soot bridges formed on the surfaceof the sensor. Next, at 420 a total soot load on the PM sensor may bedetermined based on the total length of the soot bridges determined at418. The controller may be able to determine the total soot load basedon values stored in a look-up table for example. In some examples, thecontroller may be able to calculate the soot load based on the totallength of the soot bridges.

Method 400 proceeds to 422 where it may be determined if the total sootload is higher than a threshold load, Thr. The threshold Thr, may be thethreshold load that corresponds to PM sensor regeneration threshold. Insome examples, the threshold Thr may be based on the PM load of the PMsensor above which the PM sensor may need to be regenerated. If thetotal soot load is lower than the threshold Thr, indicating that the PMsensor has not yet reached the threshold for regeneration, method 400proceeds to 424, where the soot brides may be continued to be depositedacross the electrodes, and the method returns to 410.

However if the total soot load is greater than the threshold Thr, thenmethod proceeds to 426 where the PM sensor may be regenerated asdescribed with reference to FIG. 5 and method ends. In this way,diagnostics on the DPF may be performed reliably and accurately bymeasuring and summing the length of soot bridges generated across theinterdigitated electrodes.

Thus an example method includes a method for particulate matter (PM)sensing in an exhaust flow, comprising dividing incoming PM streams inthe exhaust flow into multiple PM streams at multiple flow guidespositioned on a sensor surface between positive electrodes and negativeelectrodes of a sensor, and depositing the PM streams across thepositive electrodes and the negative electrodes forming soot bridges.Additionally or alternatively, the forming of the soot bridges mayinclude depositing the soot bridges only across the positive electrodesand the negative electrodes, and not on the flow guides. Additionally oralternatively, the flow guides may comprise evenly spaced blocksprotruding from the sensor surface of the sensor and staggered acrossalternate pairs of the positive electrodes and the negative electrodesof the sensor. Additionally or alternatively, a height of the blocks ishigher than a height of each of the positive electrodes and the negativeelectrodes of the sensor. Additionally or alternatively, the dividingmay further comprises guiding the soot bridges around the flow guidesand generating multiple soot bridge pathways around the flow guides.Additionally or alternatively, the method may further comprisedetermining a length of each of the soot bridges along each of themultiple soot bridge pathways and summing the length to determine atotal length. Additionally or alternatively, the method may furthercomprise determining a soot load of the sensor based on the total lengthand regenerating the sensor when the soot load of the sensor is higherthan a threshold load.

Turning now to FIG. 5, a method 500 for regenerating the PM sensor (suchas a PM sensor 106 shown at FIG. 1, for example) is shown. Specifically,when the soot load on the PM sensor is greater than the threshold, orwhen a resistance of the PM sensor adjusted for temperature drops to athreshold resistance, the PM sensor regeneration conditions may beconsidered met, and the PM sensor may need to be regenerated to enablefurther PM detection. At 502, regeneration of the PM sensor may beinitiated and the PM sensor may be regenerated by heating up the sensorat 504. The PM sensor may be heated by actuating a heating elementcoupled thermally to the sensor electrode surface, such as a heatingelement embedded in the sensor, until the soot load of the sensor hasbeen sufficiently reduced by oxidation of the carbon particles betweenthe electrodes. The PM sensor regeneration is typically controlled byusing timers and the timer may be set for a threshold duration at 502.Alternatively, the sensor regeneration may be controlled using atemperature measurement of the sensor tip, or by the control of power tothe heater, or any or all of these. When timer is used for PM sensorregeneration, then method 500 includes checking if the thresholdduration has elapsed at 506. If the threshold duration has not elapsed,then method 500 proceeds to 508 where the PM sensor regeneration may becontinued. If threshold duration has elapsed, then method 500 proceedsto 510 where the soot sensor regeneration may be terminated and theelectric circuit may be turned off at 512. Further, the sensorelectrodes may be cooled to the exhaust temperature for example. Method500 proceeds to 514 where the resistance between the electrodes of thePM sensor is measured. From the measured resistance, a soot bridgelength may be determined, and further the PM or soot load of the PMsensor (i.e., the accumulated PMs or soot between the electrodes of thePM sensor) may be calculated at 516 and the method proceeds to 518. At518, the calculated soot load of the PM sensor may be compared with athreshold, Lower_Thr. The threshold Lower_Thr, may be a lower threshold,lower than the regeneration threshold, for example, indicating that theelectrodes are sufficiently clean of soot particles. In one example, thethreshold may be a threshold below which regeneration may be terminated.If the soot load continues to be greater than Lower_Thr, indicating thatfurther regeneration may be required, method 500 proceeds to 508 wherePM sensor regeneration may be repeated. However, if the PM sensorcontinues to undergo repeated regenerations, the controller may seterror codes to indicate that the PM sensor may be degraded or theheating element in the soot sensor may be degraded. If the soot load islower than the threshold Lower_Thr, indicating that the electrodesurface is clean, method 500 proceeds to 520, where the soot sensorresistance and regeneration history may be updated and stored in memory.For example, a frequency of PM sensor regeneration and/or an averageduration between sensor regenerations may be updated. At 522, variousmodels may then be used by the controller to calculate the percentageefficiency of the DPF the filtration of soot. In this way, the PM sensormay perform on-board diagnosis of the DPF.

FIG. 6 illustrates an example routine 600 for diagnosing DPF functionbased on the regeneration time of the PM sensor. At 602, it may becalculated by the controller, through calibration, the time ofregeneration for the PM sensor, t(i)_regen, which is the time measuredfrom end of previous regeneration to the start of current regenerationof the PM sensor. At 604, compare t(i)_regen to t(i−1)_regen, which isthe previously calibrated time of regeneration of the PM sensor. Fromthis, it may be inferred that the soot sensor may need to cycle throughregeneration multiple times in order to diagnose the DPF. If thet(i)_regen is less than half the value of t(i−1) region, then at 608indicate DPF is leaking, and DPF degradation signal is initiated.Alternatively, or additionally to the process mentioned above, the DPFmay be diagnosed using other parameters, such as exhaust temperature,engine speed/load, etc. The degradation signal may be initiated by, forexample, a malfunction indication light on diagnostic code.

A current regeneration time of less than half of the previousregeneration time may indicate that the time for electric circuit toreach the R_regen threshold is shorter, and thus the frequency ofregeneration is higher. Higher frequency of regeneration in the PMsensor may indicate that the outflowing exhaust gas is composed of ahigher amount of particulate matter than realized with a normallyfunctionally DPF. Thus, if the change of regeneration time in the sootsensor reaches threshold, t_regen, in which the current regenerationtime of the PM sensor is less than half of that of the previousregeneration time, a DPF degradation, or leaking, is indicated, forexample via a display to an operator, and/or via setting a flag storedin non-transitory memory coupled to the processor, which may be sent toa diagnostic tool coupled to the processor. If the change ofregeneration time in the soot sensor does not reach threshold t_regen,then at 606 DPF leaking is not indicated. In this way, leaks in aparticulate filter positioned upstream of the particulate matter sensormay be detected based on a rate of deposition of the particulates on theparticulate matter sensor element.

Turning now to FIG. 7, map 700 shows an example relationship betweentotal length of soot bridges, soot load on the PM sensor and the sootload on the particulate filter. Specifically, map 700 shows a graphicaldepiction of the relationship between PM sensor regeneration and thesoot load of the DPF, specifically how PM sensor regeneration mayindicate DPF degradation. Vertical markers t0, t1, t2, t3, t4, t5 and t6identify significant times in the operation and system of PM sensor andparticulate filter.

The first plot from the top of FIG. 7 shows total length of soot bridgeformed across the surface of the PM sensor. As previously described,when PM get deposited across the interdigitated electrodes, soot bridgesmay form across the electrodes. Furthermore, due to the multiple flowguides positioned across the electrodes, multiple soot bridge pathwaymay be generated, as a result of which the length of the soot bridge maycontinue to increase (plot 710). The controller may be able to determinea soot load (plot 702) based on the total length of the soot bridges. Assuch, the total length of the soot bridge and the soot load is at itslowest value at the bottom of the plots and increases in magnitudetoward the top of the plot in the vertical direction. The horizontaldirection represents time and time increases from the left to the rightside of the plot. Horizontal marker 706 represents the threshold currentfor regeneration of the PM sensor in the top plot. Plot 704 representsthe soot load on the DPF, and the horizontal marker 708 represents thethreshold soot load of DPF in the second plot.

Between t0 and t1, a PM sensor regeneration cycle is shown. At time to,the PM sensor is in a relatively clean condition, as measured by lowtotal PM sensor current. A controller coupled to the PM sensordetermines a total length of the soot bridges by summing the length ofeach of the soot bridges formed across the multiple pathways, andfurther determines a soot load (702) of the PM sensor based on the totallength of the soot bridges. When the controller determined the soot loadto be small, it may send instructions to a regeneration circuit to endsupplying heat, so that a detection circuit may begin detecting PM loadaccumulation. As PM load increases on the sensor, soot bridges begin toform and the length of the soot bridges begin to increase. Thus, thetotal length of the soot bridges that includes summing the length ofeach of the soot bridges generated across the electrode may also beginto increase (plot 710). The controller may determine the total soot load(plot 702) on the sensor based on the total length of the soot bridges(plot 710). Between t0 and t1, PM continues to accumulate and form sootbridges across multiple pathways and the total PM load (plot 702)increases accordingly and further soot load on DPF also increases (plot704). In some examples, soot load on the DPF may be based on PM sensorload when PM sensor is located upstream of DPF, for example. Thecontroller may be able to calculate distribution of the soot bridges andfurther determine length of the soot bridges by calculating the changein current or resistance across the electrodes, for example.

At t1, the PM sensor load (plot 702) reaches the threshold load forregeneration of the PM sensor (marker 706). The threshold load forregeneration may also be based on a threshold length of soot bridges(marker 712). At t1, PM sensor regeneration may be initiated asexplained earlier. Thus, between t1 and t2, the PM sensor may beregenerated by turning on electric circuit for regeneration, forexample. At t2, the PM sensor may be sufficiently cool, and may begin toaccumulate PMs. Thus, between t2 and t3 (DPF regeneration cycle), the PMsensor may continue to accumulate PMs. During time between t2 and t3,DPF soot load continues to increase (plot 704). However, at t3, the sootload on the DPF (plot 604) reaches the threshold soot load for DPFregeneration (marker 708). Between t3 and t4, the DPF may be regeneratedto burn off the soot deposited on the DPF as explained earlier. Furtherat t4, the PM sensor regeneration frequency may be compared withprevious regeneration frequency of the PM sensor. Based on the PM sensorregeneration frequency remaining similar to previous cycles, the DPFmaybe determined to be not leaking. In this way, based on PM sensoroutput, DPF may be monitored and diagnosed for leaks.

Between t5 and t6, another DPF cycle is shown. Herein, between t5 andt6, the soot load on the DPF gradually increases (plot 704). During thistime, the total length of the soot bridges and the soot load on the PMsensor may be monitored. Plots 702 and 710 shows the PM sensor goingthrough multiple regeneration cycles as described earlier. However, thefrequency of regeneration of the PM sensor has nearly doubled (plot702). As explained earlier, higher frequency of regeneration in the PMsensor may indicate that the outflowing exhaust gas is composed of ahigher amount of particulate matter than realized with a normallyfunctionally DPF, therefore at t6, DPF leak may be indicated.

In this way, a more accurate measure of the exhaust PM load, and therebythe DPF soot load can be determined. As such, this improves theefficiency of filter regeneration operations, and reduces the need forextensive algorithms. In addition, by enabling more accurate diagnosisof an exhaust DPF, exhaust emissions compliance may be improved. Assuch, this reduces the high warranty costs of replacing functionalparticulate filters and exhaust emissions are improved and exhaustcomponent life is extended. In this way, by staggering plurality ofblocks along the surface of the sensor, soot may be distributed acrossthe surface of the sensor, and an accurate measure of the PM sensorloading may be determined. Further by using protruding electrodes on thesurface of the sensor, soot loading and soot bridge formation may beincreased. The technical effect of staggering blocks across the sensorsurface, and between the interdigitated electrodes, is that multiplepathways for the soot bridge formation may be generated. By summing thesoot bridge length across the multiple pathways and determining the sootload of the sensor, PM sensor may detect PM in the exhaust moreaccurately and hence diagnose the DPF for leaks in a more reliablefashion.

The PM sensor that has been described so far has discrete blocksstaggered between alternate pairs of contiguous interdigitatedelectrodes. Instead of staggering individual blocks across the sensorsurface, it may be possible to include contiguous rectangular blocks inbetween contiguous interdigitated electrodes in the PM sensor as shownin FIGS. 8-11. Herein, a PM sensor or assembly may include rows of flowguides arranged between a front surface and a rear surface of theassembly with a plurality of gaps formed between the flow guides. Inaddition, the PM sensor assembly may include multiple projectionsarranged between the top surface and a bottom surface of the assemblywherein the multiple projections are aligned between the plurality ofgaps as shown in FIGS. 8-11. A first example embodiment of a PM sensorassembly is described with reference to FIGS. 8 and 9A-9B, and a secondexample embodiment of the assembly is described with reference to FIGS.10 and 11.

Turning now to FIG. 8, a schematic view 800 of an example PM sensorassembly 802 (such as PM sensor 106 of FIG. 1 and/or PM sensor 202 ofFIGS. 2A-2C, and/or PM sensor 302 of FIG. 3) is shown. As explainedearlier, the PM sensor assembly 802 may be configured to measure PM massand/or concentration in the exhaust gas. The PM sensor assembly 802 maybe coupled to an exhaust passage or pipe (e.g., such as the exhaustpassage 35 shown in FIG. 1), upstream or downstream of a dieselparticulate filter (such as DPF 102 shown in FIG. 1).

In the schematic view 800, the PM sensor assembly 802 is disposed insidethe exhaust passage with exhaust gases flowing (along Z-axis) fromdownstream of the diesel particulate filter towards an exhaust tailpipe,as indicated by arrows 826. The PM sensor assembly 802 may be a box typesensor of length L, width W, and height H. The PM sensor assembly 802may include a top surface or plate 804, a bottom surface or plate 806, afront surface or plate 808, a rear surface or plate 810, a first sidesurface or plate 812, and a second, opposite side surface or plate 814.In the schematic view 800, the PM sensor assembly 802 is a cuboid witheach surface being rectangular (namely a rectangular cuboid). However,other shapes of the sensor assembly 802 are possible without deviatingfrom the scope of the disclosure. Example shapes of surfaces includesquare, hexagonal, triangular, polygonal, and the like. The distancebetween the front surface 808 and the rear surface 810 (along Z-axis) isequal to the width W of the PM sensor assembly 802. Likewise, thedistance between the top surface 804 and the bottom surface 806 (alongY-axis) constitutes the height H of the assembly 802, and the distancebetween the first side surface 812 and the second side surface 814(along X-axis) constitutes the length L of the assembly 802.

The front surface 808 and the rear surface 810 of the PM sensor assembly802 are open (e.g., not sealed) surfaces. Thus, exhaust inside theexhaust passage, enters the PM sensor assembly 802 though the frontsurface 808, and exits the assembly through the rear surface 810.Herein, the exhaust enters and exits the PM sensor assembly 802 in adirection parallel to the direction of exhaust flow (as indicated byarrow 826) inside the exhaust passage.

Inside the PM sensor assembly 802, rows of flow guides 816 are stackedalong Z-axis between the front surface 808 and the rear surface 810.Herein, each flow guide 816 is a rectangular block of length L1extending along X-axis towards the first side surface 808 and the secondside surface 814. As such, the length L1 of the flow guide 816 may belarger than each of the height h, and the width w of the flow guide. Inaddition, each rectangular block is separated from the neighboring blockby a gap 824. Hereafter, the flow guides 816 may be interchangeablyreferred to as rectangular blocks. The gap 824 between adjacent flowguides 816 includes a space with no other components there between. Thegap 824 between adjacent flow guides may be larger than or smaller thanor equal to the height h of each of the flow guide 816 without deviatingfrom the scope of the disclosure.

In summary, the PM sensor assembly 802 includes rows of flow guides 816,and a plurality of gaps 824 formed between the rows of flow guides. Asopposed to discrete set of blocks arranged inside the PM sensor assemblyas shown with reference to FIGS. 2 and 3, the PM sensor assembly 802includes stacks of continuous rectangular blocks. The rectangular blocksor flow guides 816 may be composed of material that is insulating, andnot conducting. In one example, the plurality of gaps 824 formed betweenthe rows of flow guides 816 may be uniform implying that the rows offlow guides 816 are equally spaced within the assembly. In anotherexample, the flow guides may not be equally spaced inside the assembly.In such an example, the gaps may not be the same between adjacent flowguides.

In the first example embodiment, the flow guides 816 are coupled to thebottom surface 806 of the PM sensor assembly 802. Thus, bottom portionsof all of the flow guides 816 are in face sharing contact with thebottom surface 806 of the PM sensor assembly 802. In addition, the flowguides protrude to a certain height h from the bottom surface 806 insidethe PM sensor assembly 802. As such, the height h of the flow guides maybe smaller than the height H of the PM sensor assembly 802. In oneexample, the length L1 of the flow guides 816 may be smaller than thelength L of the PM sensor assembly 802. In another example, the lengthL1 of the flow guides 812 may be equal to the length L of the PM sensorassembly 802. In such an example, the flow guides 816 may extend fromthe first side surface 812 all the way up to the second opposite sidesurface 814. Irrespective of whether L1<L or L1=L, the flow guides 816are located inside the PM sensor assembly 802, and not extending out ofthe assembly and into the exhaust passage, for example.

The soot sensing action of the PM sensor assembly 802 happens acrosspositive and negative electrodes formed on the flow guides 816. Toelucidate further, each flow guide 816 includes a positive electrode830, and a negative electrode 828 formed on opposite side surfaces ofthe flow guide. Herein, the positive electrode 830, and the negativeelectrode 828 are formed along X-axis, parallel to the front surface 808and the rear surface 810 and are arranged inside the assembly 802 suchthat a positive electrode of each flow guide faces towards a negativeelectrode of an adjacent flow guide.

To further clarify, a schematic view 900 of just the bottom potion ofthe PM sensor assembly 802 is shown in FIG. 9A. Turning now to FIG. 9A,the schematic view 900 shows the multiple flow guides 816 protrudingfrom the bottom surface 806 of the PM sensor assembly 802. The PM sensor802 includes a pair of planar continuous interdigitated electrodes 828and 830 forming a “comb” structure with the flow guide 816 positionedthere between. The properties of the electrodes 828 and 830 may besimilar to the electrodes 201 and 203 described with reference to FIGS.2A-2C. Briefly, the electrodes 828 and 830 may be manufactured frommetals such as platinum, gold, osmium, rhodium, iridium, ruthenium,aluminum, titanium, zirconium, and the like, as well as, oxides,cements, alloys and combination comprising at least one of the foregoingmetals.

Herein the electrode 828 is the negative electrode and electrode 830 isthe positive electrode. For each flow guide 816, the positive electrode830 and the negative electrode 828 are formed on opposite side surfacesof the flow guide and extend in a direction that is orthogonal todirection of exhaust flow (indicated by arrow 826). Thus, the rows offlow guides 816 are arranged such that the positive electrode 830 andthe negative electrode 828 extend horizontally along the X-axis in adirection orthogonal to the direction of exhaust flow inside the exhaustpassage. The positive electrode 830 and the negative electrode 828 mayalternatively be referred to as positive and negative tines. Herein, thepositive and negative electrodes are interdigitated across the bottomsurface 806 of the PM sensor assembly 802. Each flow guide 816 isseparated from an adjacent flow guide 816 by the gap 824. Thus, when theflow guides are arranged inside the PM sensor assembly 802, the positiveelectrode 830 of a first flow guide faces the negative electrode 828 ofa second, adjacent flow guide 816, and so on. Herein, the positiveelectrode 830 of the first flow guide 816 and the negative electrode 828of the second flow guide are separated by the gap 824. Said another way,the positive electrode 830 of the first flow guide 816 is separated bythe gap 824 from the negative electrode of the second adjacent orneighboring flow guide 816 and further separated by a distance from thenegative electrode 828 of the first flow guide. However, the distance(distance equal to width w of the flow guide, for example) between thepositive electrode 830 and the negative electrode 828 of the first flowguide includes a component namely the first flow guide, whereas thepositive electrode 830 of the first flow guide and the negativeelectrode of the second flow guide are separated by the gap which is aspace with no component in between. As such, a thickness of the positiveand negative electrodes may be much smaller than a thickness of the flowguide. Thus, the gap between the flow guides may be equal to the gapbetween the positive and negative electrodes of neighboring flow guides.Hereafter, the gap between the flow guides may be interchangeablyreferred to as the gap between the electrodes of opposite polarityformed on neighboring flow guides. Thus, when voltages are applied tothe electrodes as described below, soot particles may be accumulated inthe gap between the flow guides.

To connect the individual positive and negative electrodes of the flowguides 816, the PM sensor assembly 802 may additionally include apositive non-interdigitated electrode 834 and a negativenon-interdigitated electrode 832 formed along opposite side surfaces ofthe PM sensor assembly 802. For example, the positive non-interdigitatedelectrode 834 may be formed along the first side surface 812 in adirection parallel to the direction of exhaust flow inside the exhaustpassage (arrow 826) (refer to FIG. 8). Likewise, the negativenon-interdigitated electrode 832 may be formed along the second oppositeside surface 814 of the PM sensor assembly 802 (refer to FIG. 8). Thus,the distance between the positive non-interdigitated electrode 834 andthe negative non-interdigitated electrode 832 is equal to the length Lof the PM sensor assembly 802. In one example, the positivenon-interdigitated electrode 834 and the negative non-interdigitatedelectrode 832 may not be formed on opposite side surfaces of the PMsensor assembly 802, but rather may be located in between the twoopposite side surfaces of the PM sensor assembly 802.

Each of the positive electrodes or tines 830 formed on each of the flowguides is electrically connected to the positive non-interdigitatedelectrode 834. Likewise, each of the negative electrodes or tines 828formed on each of the flow guides is electrically connected to thenegative non-interdigitated electrode 832. Further, the positivenon-interdigitated electrode 834 may be connected to a positive terminalof a voltage source 916 of an electric circuit 936 via a connecting wire932. Similarly, the negative non-interdigitated electrode 832 may beconnected to a measurement device 918 via a connecting wire 9234, andfurther connected to a negative terminal of the voltage source 916 ofthe electric circuit 936. Thus, each pair of the positive and negativeelectrodes formed on the flow guide 916 is alternately connected topositive and negative terminal of the voltage source 916. The connectingwires 932 and 934, the voltage source 916 and the measurement device 918are part of the electric circuit 936 and are housed outside the exhaustpassage (as one example, <1 meter away). Further, the voltage source 916and the measurement device 918 of the electric circuit 236 may becontrolled by a controller, such as controller 12 of FIG. 1, so thatparticulate matter collected at the PM sensor may be used for diagnosingleaks in the DPF, for example. The measurement device 918 may be anexample of the measurement device 918 of FIG. 2A capable of reading aresistance change across the electrodes, such as a voltmeter. Asdescribed earlier with reference to FIG. 2A, as PM or soot particles getdeposited in the gap between the electrodes, the resistance between theelectrode pair may start to decrease, which is indicated by a decreasein the voltage measured by the measurement device 918. The controller 12may be able to determine the resistance between the electrodes as afunction of voltage measured by the measurement device 218 and infer acorresponding PM or soot of the PM sensor assembly 802. By monitoringthe load on the PM sensor assembly 802, the exhaust soot load downstreamof the DPF may be determined, and thereby used to diagnose and monitorthe health and functioning of the DPF.

The interdigitated portion of the negative electrode or tines 828 (ninetines shown as a non-limiting example) extend for length Ln on thebottom surface 806 of the assembly 802. Similarly, the interdigitatedportion of the positive electrode or tines 830 (nine tines shown as anon-limiting example) may extend for a length Lp on the bottom surface806 of the assembly 802. Further, the PM sensor 802 includes pluralityof protruding flow guides 816 of length L1 located between the pair ofplanar interdigitated electrodes. In one example, the length Ln and Lpof the negative and the positive electrodes may be smaller than thelength L1 of the flow guide 816. However, the lengths Ln and Lp may begreater than or equal to length L1 of the flow guide without deviatingfrom the scope of the invention.

Typical PM sensor electrodes are surface electrodes, implying that theelectrodes do not protrude from the surface of the sensor. However,these surface electrodes limit soot accumulation to just the surface ofthe sensor. To overcome the limitations of the surface electrodes, thePM sensor assembly 802 includes protruding electrodes. Herein, thepositive electrode 818 (including both the interdigitated positiveelectrodes 830, and the non-interdigitated electrode 834), and thenegative electrode 820 (including both the interdigitated negativeelectrode 828, and the non-interdigitated negative electrode 832)protrude to a certain height (h1) above the bottom surface 806 of the PMsensor assembly 802.

As described earlier, the flow guides 816 may also protrude to a heighth above the bottom surface 806 of the PM sensor assembly 802 and may becomposed of material that is insulating. In some examples, the height hof the flow guides 816 may be larger than a height h1 of the positiveand the negative electrodes. In one example, the positive and thenegative electrodes protrude to the same height h1, which may be smallerthan height h (e.g., h1<h) of the flow guides 816 above the bottomsurface 806 of the PM sensor assembly 802. In other examples, the heighth1 positive electrode 818 and the negative electrode 820 may be equal toor higher than the height h (e.g., h1>h) of the flow guides 816. As yetanother example, the height of the positive electrode 818 may bedifferent from the height of the negative electrode 820.

When a voltage is applied to the positive electrode 818 and the negativeelectrode 820 (e.g., when the controller 12 applies a certain voltage tothe positive and the negative electrodes via the voltage source 916),soot particles begin to accumulate across the bottom surface 806,specifically in the gap 824 between the interdigitated positiveelectrode 830 and the negative electrode 828.

By using protruding electrodes, soot accumulation is no longerrestricted just to the surface of the PM sensor assembly 802 (as is thecase of conventional PM sensors with surface electrodes) but is extendedto a certain height (e.g., height h1 of the electrodes) above thesurface of the assembly. Herein, the soot particles experience strongerelectrostatic fields generated between the positive and the negativeelectrodes across the gap between the electrodes, and thereforeaccumulate across he gap.

The advantage of including protruding electrodes and flow guides is thatsoot accumulation is extended over a larger region. Thus, thesensitivity of the sensor assembly to detecting incoming exhaust PM maybe increased. The inventors have recognized that it is possible tofurther increase soot accumulation by forcing the soot particles closerto the electrodes by using multiple projections coupled to the topsurface 804 of the PM sensor assembly 802 as shown in FIG. 8.

Returning to FIG. 8, the top surface 804 of the PM sensor assembly 802having multiple projections 822 is shown. Specifically, the projections822 are triangular extensions or prisms that are coupled to a bottomside of the top surface 804, and are oriented such that vertices of thetriangular extensions 822 are pointed towards the bottom surface 806 ofthe PM sensor assembly 802. Hereafter, the projections 822 may beinterchangeably referred to as triangular projections, and triangularextensions. Herein, the base of each of the triangular extensions 822 iscoupled to the top surface 804 such that the triangular extensions 822extend parallel to each of the flow guides 816, the positiveinterdigitated electrodes inside the assembly 802. As an example, thetriangular extensions 822 may extend to a length L2 parallel to theX-axis and orthogonal to the direction of exhaust flow inside theexhaust passage. In one example, the length L2 of the triangularextensions may be equal to the length L1 of the flow guides 816. Thevertices of each of the triangular extensions 822 are aligned betweenthe plurality of gaps 824 formed between the multiple rows of flowguides 816. A side view of the PM sensor assembly 802 is shown in FIG.9B.

Turning now to FIG. 9B, a side view 950 of a portion of the PM sensorassembly 802 is shown. Specifically, exhaust flows from the upstreamside of the PM sensor assembly 802 towards the downstream side along thedirection indicated by arrows 952. The flow guides 816 are coupled tothe bottom surface 806, and the triangular projections 822 are coupledto the top surface 804 of the PM sensor assembly 802. In addition, theflow guides 816 are separated from successive flow guides by the gap824, and each flow guide 816 includes a positive electrode 830 and anegative electrode 828 formed on either sides. Thus, electrodes ofopposite polarity formed on the sides of adjacent flow guides areseparated by the gap 824. When the controller 12 applies a voltage tothe positive and the negative electrodes, soot particles may beaccumulated in the gap 824 between the positive electrode and thenegative electrode formed on adjacent flow guides 816, as describedearlier.

Additionally, the triangular projections or extensions 822 may extendinto the gap 824 as shown in view 950 forming channels 910 through whichthe exhaust can flow. Each triangular extension includes a base b, avertex v, and a height h2. As previously described, the base b of eachof the triangular extensions 822 is coupled to the bottom side of thetop plate 804. As such, the triangular projections 822 may be separatedfrom each other by a distance d. In one example, the distance d may beequal to the width w of the flow guide 816, and the base b may be equalto the gap 824. In another example, the distance d may not be equal tothe width w, and the base b may not be equal to the gap 824. Thetriangular cross section of the triangular extensions may beequilateral, isosceles, or scalar, without deviating from the scope ofthe disclosure. However, other geometries of the projections may bepossible. As an example, the projections may have a hexagonal crosssection, or polygonal cross section.

The vertex v of each of the triangular extension 822 extends to acertain distance in the gap 824 towards the bottom surface 806 of the PMsensor assembly 802, thereby forming the channels 910. Each channel 910may be smaller than the gap 824, for example. In one example, thetriangular extensions 822 may extend halfway into the gap 824, such thatthe vertex v of the triangular extension 822 is at a distance equal toh/2 from the bottom surface 806. In another example, the vertex v may beat a distance that is about h/3 from the bottom surface 806. Thetriangular extensions 822 extending into the gap 824 between adjacentflow guides 816 may generate a physical force on the soot particles,thereby mechanically forcing the soot particles closer to the bottomsurface 806 of the PM sensor assembly 802. The soot particles traversein between the gap 822 along a trajectory shown by dashed arrow 906.Incoming soot particles deflect off the sides of the triangles, weaveinto the channel 910 between the extension 822 and the flow guide 816,moving closer to the gap 824, where the soot particles (908) areeventually deposited. Exhaust then exits the assembly through the rearsurface 810.

The advantage of pushing the soot particles closer to the bottom surface806 is that the soot particles are trapped between the positiveelectrodes and negative electrodes of adjacent flow guides 822 for alonger time. This in turn ensures that a retention or hold time of thesoot particles in the gap is increased thereby increasing theprobability of capture of the soot particles in the gap 824. In thisway, the amount of soot particles accumulated in the gap between theelectrodes of the PM sensor assembly 802 may be increased. The exhaustmay exit the PM sensor assembly on the downstream side via the rear opensurface 810 (as shown in FIG. 8).

The PM sensor assembly 802 may include a heating element (not shown) andthe PM sensor assembly may be regenerated by heating the assembly viathe heating element to burn the accumulated soot particles from thesurface of the assembly. In an alternate example, the heating elementmay be coupled to each of the flow guides. By intermittentlyregenerating the PM sensor assembly, it may be returned to a conditionmore suitable for collecting exhaust soot. In addition, accurateinformation pertaining to the exhaust soot level may be inferred fromthe sensor regeneration and relayed to the controller.

A second example embodiment of the sensor assembly is shown in FIGS. 10and 11. Turning now to FIG. 10, a schematic view 1000 of a PM sensorassembly 1002 is shown. The PM sensor assembly 1002 may be an example ofthe PM sensor assembly 802 described in FIGS. 8, 9A, and 9B, and may bedisposed in an exhaust passage such that exhaust gas flows along Z-axisinto the assembly as indicated by arrows 1026. As such, the details ofthe sensor assembly 1002 may be similar to the assembly 802.

Similar to the PM sensor assembly 802 described with reference to FIGS.8, 9A, and 9B, the PM sensor assembly 1002 may be a box type sensor oflength L, width W, and height H. The PM sensor assembly 1002 may includea top surface or plate 1004, a bottom surface or plate 1006, a frontsurface or plate 1008, a rear surface or plate 1010, a first sidesurface or plate 1012, and a second, opposite side surface or plate1014. The front surface 1008 and the rear surface 1010 of the PM sensorassembly 1002 are open (e.g., not sealed) surfaces. Thus, exhaust insidethe exhaust passage, enters the PM sensor assembly 1002 though the frontsurface 1008, and exits the assembly through the rear surface 810.Herein, the exhaust enters and exits the PM sensor assembly 1002 in adirection parallel to the direction of exhaust flow (as indicated byarrow 1026) inside the exhaust passage.

Inside the PM sensor assembly 1002, multiple flow guides 1016 stackedalong Z-axis between the front surface 1008 and the rear surface 1010.Thus, exhaust enters the sensor assembly or box via the front surface1008, exhaust then weaves across the plurality of flow guides 1016 andexits the sensor assembly via the rear surface 1010. In contrast to theflow guides 816 of FIG. 8, the flow guides 1016 are not coupled to thebottom surface 1006. Herein, the flow guides 1016 are suspended withinthe assembly 1002 between the top surface 1004 and the bottom surface1006 if the assembly 1002. In addition, one end of each of the flowguides 1016 is coupled to the first side surface 1012, and the oppositeend of each of the flow guides 1016 is coupled to the second, oppositeside surface 1014.

Each flow guide 1016 is a rectangular block of length L extending alongX-axis from the first side surface 1012 and the second side surface1014. In addition, each rectangular block is separated from theneighboring block by a gap 1024. Hereafter, the flow guides 1016 may beinterchangeably referred to as rectangular blocks. The gap 1024 betweenadjacent flow guides 1016 includes a space with no other componentsthere between. The gap 1024 between adjacent flow guides may be largerthan or smaller than or equal to the height h of each of the flow guide816 without deviating from the scope of the disclosure.

The flow guides 1016 may include positive electrodes 1030 formed alongone side surface of the flow guide, and may additionally includenegative electrode 1028 formed along the opposite side surface of theflow guide. Similar to the PM sensor assembly 802, the flow guides 1016may be arranged such that the positive electrode 1030 of each of theflow guide 1016 faces towards the negative electrode 1028 of theadjacent flow guide 1016. In this way, the electrodes of oppositepolarity may face towards one another in the gap 1026. Thus, when thecontroller 12 applies a voltage to the electrodes, soot particles may becaptured in the gap between the electrodes, as described in detail withreference to FIGS. 8, 9A, and 9B.

The PM sensor assembly 1002 includes multiple projections 1022. Herein,the projections 1022 are formed above and below the flow guides 1016 asshown in FIG. 11. Turning now to FIG. 11, a side view 1100 of a portionof the PM sensor assembly 1002 is shown. Specifically, exhaust flowsfrom the upstream side of the PM sensor assembly 1002 towards thedownstream side along the direction indicated by arrows 1105. The flowguides 1016 are suspended between the top surface 1004, and the bottomsurface 1006. The positive electrodes 1030 are connected to a positiveterminal of a voltage source (not shown) via a connecting wire 1034.Similarly, the negative electrodes 1028 are connected to a negativeterminal of the voltage source via a connecting wire 1032. As describedwith reference to FIG. 9A, the PM sensor assembly 1002 may include anelectric circuit comprising the voltage source, and a measurement device(not shown) that are housed outside the exhaust passage (as one example,<1 meter away). The controller 12 may be able to determine theresistance between the electrodes as a function of voltage measured bythe measurement device and infer a corresponding PM or soot load of thePM sensor assembly 1002. By monitoring the load on the PM sensor 1002,the exhaust soot load downstream of the DPF may be determined, andthereby used to diagnose and monitor the health and functioning of theDPF.

The PM sensor assembly 1002 may include a heating element 1020 and thePM sensor assembly may be regenerated by heating the assembly via theheating element to burn the accumulated soot particles from the surfaceof the assembly. By intermittently regenerating the PM sensor assembly,it may be returned to a condition more suitable for collecting exhaustsoot. In addition, accurate information pertaining to the exhaust sootlevel may be inferred from the sensor regeneration and relayed to thecontroller.

The PM sensor assembly 1002 includes multiple triangular projections1022 formed along the top and bottom side of the flow guides 1016.Herein, the triangular projections 1022 include a first set oftriangular shields 1102 connecting alternate pairs of flow guides 1016along a top side, and a second set of triangular shields 1104 connectingcomplementary pairs of flow guides along a bottom side.

Each triangular shield couples two adjacent flow guides forming a vertexthat extends away from the flow guides, towards either the top surfaceor the bottom surface of the assembly. Each triangular shield 1102 formsa gable-shaped region 1110 contiguous with the gap 1024 between adjacentflow guides. Together, the gable-shaped region 1110 and the gap 1024form a channel through which exhaust flows. Likewise, each triangularshield 1104 forms a gable-shaped region 1112 contiguous with the gap1024 between adjacent flow guides. Together, the gable-shaped region1112 and the gap 1024 form a channel through which exhaust flows.However, the gable-shaped region 1110 formed by the first set oftriangular shields 1102 is not contiguous with the gable-shaped regions

As an example, the first triangular shield 1102 couples a first flowguide and a second flow guide of the assembly 1002, the first triangularshield extending towards the top surface 1004 of the assembly, andwherein a second triangular shield 1104 couples the first flow guide toa third flow guide of the assembly, the second triangular shieldextending towards the bottom surface 1006 of the assembly, and whereinthe second flow guide and the third flow guide are located on twoopposite sides of the first flow guide.

The advantage of including projections in the form of shields extendingtowards the top or bottom surface of the assembly is that the incomingexhaust may be divided into two streams. Thus, exhaust from the exhaustpassage entering the assembly 1002 via the front surface (as indicatedby arrows 1105) is divided into a top flow 1106, and a bottom flow 1108by the flow guides and the triangular shields. Specifically, the topflow 1106 includes exhaust flowing within (or below) the top surface1004, and further into the gap 1024, and the gable-shaped region 1112formed by the second set of triangular shields 1104. Likewise, thebottom flow 1108 includes exhaust flowing above the bottom surface 1006,and further into the gap 1024, and the gable-shaped region 1110 formedby the first set of triangular shields 1102. Herein, the top flow 1106includes exhaust flowing between the top surface 1004 of the assemblyand the flow guides 1016, and the bottom flow 1108 includes exhaustflowing between the bottom surface 1006 of the assembly and the flowguides 1016. In this way, exhaust is directed towards the gap betweenthe positive electrode and the negative electrode, and soot particles1114 in the exhaust are captured in the gap 1024 between the electrodes.Thus, exhaust may be able to circulate longer in the region enclosedwithin the triangular shields, specifically in the gap between theelectrodes, thereby increasing the amount of particulates capturedacross the electrodes in the gap. In addition, the soot particles 1114may deflect off the sides of the triangular projections, and may flowinto the gap between the electrodes. In this way, a retention time ofthe soot particles inside the gap may be increased. Overall, thesecharacteristics of the sensor assembly may cause an output of the sensorassembly to be more accurate, thereby increasing the accuracy ofestimating particulate loading on a particulate filter.

Thus, a first example sensor assembly includes multiple rows of flowguides arranged between a front surface and a rear surface of theassembly, each flow guide having a positive electrode and a negativeelectrode formed along opposite surfaces of the flow guide, a pluralityof gaps formed between the flow guides; and multiple projectionsarranged between a top surface and a bottom surface of the assembly, themultiple projections aligned between the plurality of gaps. Additionallyor alternatively, the positive electrode of each flow guide may facetowards the negative electrode of an adjacent flow guide and may beseparated from the negative electrode of the adjacent flow guide by agap of the plurality of gaps. Additionally or alternatively, each flowguide may comprises a rectangular block extending from one side surfaceto an opposite side surface of the assembly, and wherein the positiveelectrode and the negative electrode may extend to a certain lengthalong opposite surfaces of the rectangular block. Additionally oralternatively, each of the flow guide, the positive electrode, and thenegative electrode may protrude from the bottom surface of the assembly,and wherein the multiple projections are coupled to the top surface ofthe assembly, each of the multiple projections projecting into the gapbetween adjacent flow guides. Additionally or alternatively, themultiple projections may comprise triangular extensions, bases of thetriangular extensions coupling the triangular extensions to the topsurface of the assembly, and vertices of the triangular extensionsextending into the gap between adjacent flow guides, and wherein exhaustfrom an exhaust passage entering the assembly via the front surface ofthe assembly may be directed over the rows of flow guides and pushedcloser towards the gap between the positive electrode and the negativeelectrode of adjacent flow guides by the triangular extensions and theexhaust and subsequently exits the assembly via the rear surface of theassembly. Additionally or alternatively, the rows of flow guides may besuspended within the assembly between the top surface and the bottomsurface of the assembly and further coupled from one side surface to anopposite side surface of the assembly, and wherein the multipleprojections may include triangular shields alternating in a direction ofprojection, the multiple projections coupled to the rows of flow guides.Additionally or alternatively, each triangular shield may form agable-shaped region contiguous with the gap between adjacent flowguides. Additionally or alternatively, a first triangular shield maycouple a first flow guide and a second flow guide of the assembly, thefirst triangular shield extending towards the top surface of theassembly, and wherein a second triangular shield may couple the firstflow guide to a third flow guide of the assembly, the second triangularshield extending towards the bottom surface of the assembly, and whereinthe second flow guide and the third flow guide are located on twoopposite sides of the first flow guide. Additionally or alternatively,exhaust from an exhaust passage entering the assembly via the frontsurface may be divided into a top flow and a bottom flow by the flowguides and the triangular shields and may be directed towards the gapbetween the positive electrode and the negative electrode, the top flowcomprising exhaust flowing between the top surface of the assembly andthe flow guides, and the bottom flow comprising exhaust flowing betweenthe bottom surface of the assembly and the flow guides. Additionally oralternatively, the assembly may comprise a heating element coupled toeach of the flow guides and a controller with computer readableinstructions stored on non-transitory memory for during exhaust flow,applying a first voltage to the positive electrode and the negativeelectrode of each of the flow guides to accumulate exhaust particulatematter in the exhaust flow across the gap between the positive electrodeand negative electrode formed on neighboring flow guides, estimating aload on the particulate matter sensor assembly based on a currentgenerated across the positive and the negative electrode; and responsiveto the load being higher than a threshold, applying a second voltage tothe heating element of the sensor assembly to regenerate the sensorassembly.

A second example particulate matter (PM) sensor assembly may include aplurality of rectangular blocks separated by a gap arranged inside asensor housing, positive electrode and negative electrode formed alongtwo opposite, parallel surfaces of each of the rectangular blocks,electrodes of opposite polarity formed on neighboring blocks facingtowards the gap, and a plurality of triangular projections formed insidethe sensor housing aligned with the gap formed between adjacentrectangular blocks. Additionally or alternatively, the sensor box may becoupled to an exhaust passage such that exhaust may enter the sensorbox, may deflect off surfaces of the plurality of triangularprojections, and may flow into the gap, particulate matter in theexhaust may collect across the gap in between the positive electrode andthe negative electrode of adjacent rectangular blocks, exhaust weavesacross the plurality of rectangular blocks and exits the sensor box.

Turning now to FIG. 12, a method 1200 for directing exhaust intochannels or gaps formed between adjacent flow guides of the PM sensorassembly (such as a PM sensor assembly 802 shown at FIGS. 8, 9A, and 9B,and/or PM sensor assembly 1002 of FIGS. 10, and 11, for example) isshown. Specifically, the PM sensor assembly may be a sensor boxincluding multiple flow guides positioned within the box (or housing).

Instructions for carrying out method 1200 may be executed by acontroller based on instructions stored on a memory of the controllerand in conjunction with signals received from sensors of the enginesystem, such as the sensors described above with reference to FIG. 1.The controller may employ engine actuators of the engine system toadjust engine operation, according to the methods described below.

At 1202, method 1200 includes determining and/or estimating engineoperating conditions including exhaust flow conditions. Engine operatingconditions determined may include, for example, engine speed, exhaustflow direction, exhaust flow rate, engine temperature, exhaust air-fuelratio, exhaust temperature, duration (or distance) elapsed since a lastregeneration of the DPF, PM load on PM sensor, boost level, ambientconditions such as barometric pressure and ambient temperature, etc.Exhaust flow conditions include estimating or sensing one or more ofsoot load of PM sensor assembly, exhaust flow rate, exhaust flowdirection, exhaust temperature, and the like.

Method 1200 proceeds to 1204 where the method includes flowing exhaustfrom an exhaust passage into a PM sensor assembly (such as PM sensorassembly 802 of FIGS. 8, 9A, and 9B and/or PM sensor assembly 1002 ofFIGS. 10 and 11). As described earlier, the PM sensor assembly may be asensor box with an open front plate or surface through which exhaust mayenter the assembly. As described earlier, exhaust may enter the assemblyin a direction parallel to the direction of flow of exhaust inside theexhaust passage. Method proceeds to 1206.

At 1206, method 1200 includes directing the exhaust into channels formedbetween rectangular blocks of the assembly. Specifically, the channelsare formed by projections extending in the gap between rectangularblocks. Directing the exhaust into the channels includes deflectingexhaust off projections into the channels to increase a retention orhold time of the exhaust PM in the channels at 1208. In one exampleembodiment, the projections include triangular prisms or extensionsformed on the top plate of the assembly and extending into the gap orchannels formed between the blocks, wherein the blocks are coupled tothe bottom plate of the assembly. Herein, the base of the triangularprism may rest on a surface of the top plate, and the triangular prismmay be formed along the top plate in a direction parallel to a length ofthe rectangular blocks, the length being perpendicular to the directionof exhaust flow inside the exhaust passage. Thus, deflecting the exhaustoff projections include deflecting the exhaust off the sides of thetriangular prisms at 1210. In an alternate embodiment, the projectionsmay include triangular shields coupling alternate blocks along the topand bottom; the rectangular blocks are suspended in between the top andthe bottom plate of the assembly. Herein, the projections includes afirst set of triangular shields connecting adjacent rectangular blocksvia a top side, and a second set of triangular shields connectingalternate adjacent rectangular blocks via a bottom side, the first setof triangular shields and the second set of triangular shields includingvertices extending in opposite directions away from the channels. Inaddition, the first set of triangular shields, and the second set oftriangular shields alternate in a direction of projection. In such anembodiment, deflecting exhaust off the projections may includedeflecting exhaust off the triangular shields that are alternating in adirection of projection at 1212.

In addition, method 1200 includes weaving the exhaust around therectangular blocks at 1214. As explained earlier, in one exampleembodiment, the rectangular blocks are coupled to the bottom plate ofthe assembly. In an alternate embodiment, the rectangular blocks aresuspended between the top and bottom plate of the assembly. Methodproceeds to 1216.

At 1216, method 1200 includes streaming the exhaust out of the assemblyvia a rear open plate. Herein, the rear plate is located opposite to thefront plate. The rear plate is configured to direct the exhaust out ofthe PM sensor assembly in a direction parallel to exhaust flow insidethe exhaust passage. Thus, exhaust enters and exits the PM sensorassembly in a similar way, in a direction parallel to the direction ofexhaust flow inside the exhaust passage. Method proceeds to 1218.

At 1218, method 1200 includes collecting exhaust PM or soot in thechannel between electrodes of opposite polarity formed on adjacentrectangular blocks, and calculating a soot load of the assembly. Asexplained earlier, positive and negative electrodes are formed onopposite side surfaces of the rectangular blocks. In one example, wherethe blocks are coupled to the bottom plate of the assembly, the blocksas well as the electrodes protrude from the bottom surface of theassembly. The blocks are arranged inside the assembly such that thepositive electrode formed on the side of a block faces towards anegative electrode formed along a side of an adjacent block. Thecontroller applies a first voltage to the electrodes to accumulate PMacross the electrodes. As PM or soot particles get deposited between theelectrodes, the current measured between the electrodes may start toincrease, which is measured by a measurement device. The controller maybe able to determine the current and infer a corresponding PM or sootload on the PM sensor assembly. By monitoring the load on the sensorelement, the exhaust soot load downstream of the DPF may be determined,and thereby used to diagnose and monitor the health and functioning ofthe DPF. Method proceeds to 1220.

At 1220, method 1200 includes checking if the soot load is higher than athreshold. The threshold may be indicative of sensor regenerationconditions. When the soot load on the PM sensor assembly is greater thanthe threshold, PM sensor regeneration conditions may be considered met,and the PM sensor assembly may need regeneration. If the soot load ishigher than the threshold (e.g., “YES” at 1220), then method 1200proceeds to 1226 where the PM sensor assembly may be regenerated byperforming a method described in FIG. 5. Briefly, regeneration of the PMsensor assembly may be initiated by heating up the sensor. The PM sensorassembly may be heated by actuating a heating element coupled thermallyto the blocks of the assembly, for example. Herein, the controller mayclose the switch in a regeneration circuit, thereby applying a voltage(e.g., a second different voltage) to the heating element, causing theheating elements to heat up. Further, the controller may not applyvoltages to the sensor electrodes while regenerating the sensor. Thus,the sensor electrodes may not accumulate soot during the sensorregeneration. As such, the heating element may be actuated until thesoot load of the sensor has been sufficiently reduced by oxidation ofthe carbon particles between the electrodes. However, if soot load islower than the threshold (e.g., “NO” at 1220), then method 1200 proceedsto 1224 where PM may continue to be collected in the channel between therectangular blocks, and the method returns. In this way, by flowing theexhaust into the channels and increasing the retention time,accumulation of PM across the electrodes of the assembly may beincreased.

The technical effect of including the triangular prisms is to exert amechanical force on the incoming soot particles and push them closer tothe electrodes where the soot particles may experience a greaterelectrostatic force. In this way, more of the incoming soot particulatesmay be captured by the sensor assembly. The technical effect ofincluding triangular shields is to circulate the soot particulates for alonger duration in the region enclosed within the triangular shields,specifically in the gap between the electrodes, thereby increasing theamount of particulates captured across the electrodes in the gap.Overall, these characteristics of the sensor assembly may cause anoutput of the sensor assembly to be more accurate, thereby increasingthe accuracy of estimating particulate loading on a particulate filter.

The systems and methods described above also provide for a particulatematter sensor, comprising a pair of planar interdigitated electrodesspaced at a distance from each other and protruding from a surface ofthe PM sensor, and a plurality of protruding flow guides located betweenthe pair of planar interdigitated electrodes. In a first example of theparticulate matter sensor, the sensor may additionally or alternativelyinclude wherein the flow guides includes evenly spaced blocks arrangedbetween pairs of tines of the interdigitated electrodes, spacing betweenthe blocks being smaller than a distance between the pairs of tines ofthe pair of planar interdigitated electrodes. A second example of the PMsensor optionally includes the first example and further includeswherein the blocks are further staggered between alternate pairs oftines of the interdigitated electrodes. A third example of the PM sensoroptionally includes one or more of the first and the second examples,and further includes wherein each alternate pair of tines include blocksarranged with less than threshold overlap with blocks in precedingalternating pairs of tines. A fourth example of the PM sensor optionallyincludes one or more of the first through the third examples, andfurther includes, wherein a spacing between the blocks between the pairsof tines is lower than a separation between the pairs of tines of theinterdigitated electrodes. A fifth example of the PM sensor optionallyincludes one or more of the first through the fourth examples, andfurther includes, wherein a height of the blocks is larger than a heightof each of the pairs of tines of the interdigitated electrodes. A sixthexample of the PM sensor optionally includes one or more of the firstthrough the fifth examples, and further includes wherein the pairs oftines of the interdigitated electrodes are positioned orthogonal toexhaust flow, and wherein each pair of tines are alternately connectedto positive and negative terminal of a voltage source. A seventh exampleof the PM sensor optionally includes one or more of the first throughthe third examples, and further includes wherein soot in the exhaustflow deposits between the pairs of tines of the interdigitatedelectrodes avoiding the blocks positioned between the pairs of tines. Aneighth example of the PM sensor optionally includes one or more of thefirst through the third examples, and further includes a controller withcomputer-readable instructions stored on non-transitory memory fordividing a single stream of PM in the exhaust flow into multiple streamsof PM at each of the blocks located between the pairs of tines of theinterdigitated electrodes, depositing the PM multiple streams of PM onthe pairs of tines, and regenerating the PM sensor when a PM loadbetween the pairs of tines reaches a threshold PM load.

The systems and methods described above also provide for a particulatematter sensor, comprising a pair of continuous interdigitated electrodesformed on a sensor surface including a plurality of uniformly spacedprotruding blocks positioned in a staggered arrangement along the sensorsurface, the protruding blocks positioned in between alternate pairs ofthe interdigitated electrodes. In a first example of the particulatematter sensor, the sensor may additionally or alternatively includewherein a height of each of the blocks is greater that a height of eachof the interdigitated electrodes. A second example of the PM sensoroptionally includes the first example and further includes wherein alength of each of the blocks is smaller than a length of each of theinterdigitated electrodes. A third example of the PM sensor optionallyincludes one or more of the first and the second examples, and furtherincludes a controller with computer-readable instructions stored onnon-transitory memory for accumulating soot across the pair ofcontinuous interdigitated electrodes and avoiding accumulating soot onthe blocks, determining a soot load on the PM sensor based on a sumtotal of soot accumulated across the pair of interdigitated electrodes;and regenerating the PM sensor when the soot load is higher than athreshold.

The systems and methods described above also provide for a method ofparticulate matter sensing in an exhaust flow, comprising dividingincoming PM streams in the exhaust flow into multiple PM streams atmultiple flow guides positioned on a sensor surface between positiveelectrodes and negative electrodes of a sensor, and depositing the PMstreams across the positive electrodes and the negative electrodesforming soot bridges. In a first example of the method, the method mayadditionally or alternatively include wherein the forming of the sootbridges includes depositing the soot bridges only across the positiveelectrodes and the negative electrodes, and not on the flow guides. Asecond example of the method optionally includes the first example, andfurther includes wherein the flow guides comprise evenly spaced blocksprotruding from the sensor surface of the sensor and staggered acrossalternate pairs of the positive electrodes and the negative electrodesof the sensor. A third example of the method optionally includes one ormore of the first and the second examples, and further includes whereina height of the blocks is higher than a height of the each of thepositive electrodes and the negative electrodes of the sensor. A fourthexample of the method optionally includes one or more of the firstthrough the third examples, and further includes wherein the dividingfurther comprises guiding the soot bridges around the flow guides andgenerating multiple soot bridge pathways around the flow guides. A fifthexample of the method optionally includes one or more of the firstthrough the fourth examples, and further includes determining a lengthof each of the soot bridges along each of the multiple soot bridgepathways and summing the length to determine a total length. A sixthexample of the method optionally includes one or more of the firstthrough the fifth examples, and further comprising determining a sootload of the sensor based on the total length and regenerating the sensorwhen the soot load of the sensor is higher than a threshold load.

The systems and methods described above provide for a particulate mattersensor assembly comprising rows of flow guides arranged between a frontsurface and a rear surface of the assembly, each flow guide having apositive electrode and a negative electrode formed along oppositesurfaces of the flow guide, a plurality of gaps formed between the rowsof flow guides; and multiple projections arranged between a top surfaceand a bottom surface of the assembly, the multiple projections alignedbetween the plurality of gaps. In a first example of the particulatematter sensor assembly, the assembly may additionally or alternativelywherein the positive electrode of each flow guide faces towards thenegative electrode of an adjacent flow guide and is separated from thenegative electrode of the adjacent flow guide by a gap of the pluralityof gaps. A second example of the particulate matter sensor assemblyoptionally includes the first example and further includes wherein eachflow guide comprises a rectangular block extending from one side surfaceto an opposite side surface of the assembly, and wherein the positiveelectrode and the negative electrode extend to a certain length alongopposite surfaces of the rectangular block. A third example of theparticulate matter sensor assembly optionally includes one or more ofthe first and the second examples, and further includes wherein each ofthe flow guide, the positive electrode, and the negative electrodeprotrude from the bottom surface of the assembly, and wherein themultiple projections are coupled to the top surface of the assembly,each of the multiple projections projecting into the gap betweenadjacent flow guides. A fourth example of the assembly optionallyincludes one or more of the first through the third examples, andfurther includes wherein the multiple projections comprise triangularextensions, bases of the triangular extensions coupling the triangularextensions to the top surface of the assembly, and vertices of thetriangular extensions extending into the gap between adjacent flowguides, and wherein exhaust from an exhaust passage entering theassembly via the front surface of the assembly is directed over the rowsof flow guides and pushed closer towards the gap between the positiveelectrode and the negative electrode of adjacent flow guides by thetriangular extensions and the exhaust and subsequently exits theassembly via the rear surface of the assembly. A fifth example of theassembly optionally includes one or more of the first through the fourthexamples, and further includes wherein the rows of flow guides aresuspended within the assembly between the top surface and the bottomsurface of the assembly and further coupled from one side surface to anopposite side surface of the assembly, and wherein the multipleprojections include triangular shields alternating in a direction ofprojection, the multiple projections coupled to the rows of flow guides.A sixth example of the assembly includes one or more of the firstthrough the fifth examples, and further includes wherein each triangularshield forms a gable-shaped region contiguous with the gap betweenadjacent flow guides. A seventh example of the assembly includes one ormore of the first through the sixth examples, and further includeswherein a first triangular shield couples a first flow guide and asecond flow guide of the assembly, the first triangular shield extendingtowards the top surface of the assembly, and wherein a second triangularshield couples the first flow guide to a third flow guide of theassembly, the second triangular shield extending towards the bottomsurface of the assembly, and wherein the second flow guide and the thirdflow guide are located on two opposite sides of the first flow guide. Aneighth example of the assembly includes one or more of the first throughthe seventh examples, and further includes wherein exhaust from anexhaust passage entering the assembly via the front surface is dividedinto a top flow and a bottom flow by the flow guides and the triangularshields and directed towards the gap between the positive electrode andthe negative electrode, the top flow comprising exhaust flowing betweenthe top surface of the assembly and the flow guides, and the bottom flowcomprising exhaust flowing between the bottom surface of the assemblyand the flow guides. A ninth example of the assembly includes one ormore of the first through the eighth examples, and further includes aheating element coupled to each of the flow guides and a controller withcomputer readable instructions stored on non-transitory memory forduring exhaust flow, applying a first voltage to the positive electrodeand the negative electrode of each of the flow guides to accumulateexhaust particulate matter in the exhaust flow across the gap betweenthe positive electrode and negative electrode formed on neighboring flowguides, estimating a load on the particulate matter sensor assemblybased on a current generated across the positive and the negativeelectrode, and responsive to the load being higher than a threshold,applying a second voltage to the heating element of the sensor assemblyto regenerate the sensor assembly.

The systems and methods described above also provide for a method, themethod comprising flowing exhaust from an exhaust passage through aparticulate matter sensor assembly, the flowing including directing theexhaust into channels formed between rectangular blocks of the assemblythrough projections extending in the channels, the rectangular blockshaving positive and negative electrodes formed along two opposite sidesurfaces. In a first example of the method, the method may additionallyor alternatively include wherein the directing further comprises flowingthe exhaust into the sensor assembly through a front open plate in adirection parallel to exhaust flow inside the exhaust passage,deflecting the exhaust off the projections into the channels andincreasing a retention time of exhaust particulate matter in thechannels, weaving the exhaust around the rectangular blocks, andstreaming the exhaust out of the assembly via a rear open plate in adirection parallel to the direction of flow of exhaust inside theexhaust passage, the rear open plate and the front open plate positionedat opposite ends of the assembly. A second example of the methodoptionally includes the first example, and further includes wherein eachof the projections includes a triangular prism formed on a top plate ofthe assembly, a vertex of the triangular prism extending into thechannels formed between adjacent rectangular blocks, and a base of thetriangular prism resting on a surface of the top plate, and wherein thetriangular prism is formed along the top plate in a direction parallelto a length of the rectangular blocks, the length perpendicular to thedirection of exhaust flow inside the exhaust passage. A third example ofthe method optionally includes one or more of the first and the secondexamples, and further includes wherein the rectangular blocks protrudefrom a bottom plate towards the top plate of the assembly, and whereinthe positive and the negative electrodes formed protrude from the bottomplate of the assembly. A fourth example of the method optionallyincludes one or more of the first through the third examples, andfurther includes wherein the rectangular blocks are suspended in betweena top plate and a bottom plate of the assembly, and wherein therectangular blocks extend from one side plate of the assembly towards anopposite side plate of the assembly. A fifth example of the methodoptionally includes one or more of the first through the fourthexamples, and further includes wherein the projections includes a firstset of triangular shields connecting adjacent rectangular blocks via atop side, and a second set of triangular shields connecting alternateadjacent rectangular blocks via a bottom side, the first set oftriangular shields and the second set of triangular shields includingvertices extending in opposite directions away from the channels. Asixth example of the method optionally includes one or more of the firstthrough the fifth examples, and further includes wherein the first setof triangular shields, and the second set of triangular shieldsalternate in a direction of projection.

The systems and methods described above provide for a particulate mattersensor assembly, comprising a plurality of rectangular blocks separatedby a gap arranged inside a sensor housing, positive electrode andnegative electrode formed along two opposite, parallel surfaces of eachof the rectangular blocks, electrodes of opposite polarity formed onneighboring blocks facing towards the gap, and a plurality of triangularprojections formed inside the sensor housing aligned with the gap formedbetween adjacent rectangular blocks. In a first example of theparticulate matter sensor assembly, the sensor may additionally oralternatively include wherein the sensor box is coupled to an exhaustpassage such that exhaust enters the sensor box, deflects off surfacesof the plurality of triangular projections and flows into the gap,particulate matter in the exhaust collects across the gap in between thepositive electrode and the negative electrode of adjacent rectangularblocks, exhaust weaves across the plurality of rectangular blocks andexits the sensor box.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.Selected actions of the control methods and routines disclosed hereinmay be stored as executable instructions in non-transitory memory andmay be carried out by the control system including the controller incombination with the various sensors, actuators, and other enginehardware. The specific routines described herein may represent one ormore of any number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various actions, operations, and/or functions illustrated may beperformed in the sequence illustrated, in parallel, or in some casesomitted. Likewise, the order of processing is not necessarily requiredto achieve the features and advantages of the example embodimentsdescribed herein, but is provided for ease of illustration anddescription. One or more of the illustrated actions, operations and/orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, the described actions, operations and/orfunctions may graphically represent code to be programmed intonon-transitory memory of the computer readable storage medium in theengine control system, where the described actions are carried out byexecuting the instructions in a system including the various enginehardware components in combination with the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A sensor assembly, comprising: rows of flowguides arranged between a front surface and a rear surface of theassembly, each flow guide having a positive electrode and a negativeelectrode formed along different surfaces of the flow guide, where thedifferent surfaces are opposite left and right side surfaces of the flowguide; a plurality of gaps formed between the rows of flow guides; andmultiple projections arranged between a top surface and a bottom surfaceof the assembly, wherein the multiple projections are triangularextensions that are each positioned inside the plurality of gaps, andwherein an axis of a vertex of each triangular extension and an axis ofeach of the flow guides overlap one another within the plurality ofgaps.
 2. The assembly of claim 1, wherein bases of the triangularextensions couple the triangular extensions to the top surface of theassembly, and wherein exhaust from an exhaust passage entering theassembly via the front surface of the assembly is directed over the rowsof flow guides and pushed closer towards the gap between the positiveelectrode and the negative electrode of adjacent flow guides by thetriangular extensions and the exhaust and subsequently exits theassembly via the rear surface of the assembly.
 3. The assembly of claim1, wherein the positive electrode of each flow guide faces towards thenegative electrode of an adjacent flow guide and is separated from thenegative electrode of the adjacent flow guide by a gap of the pluralityof gaps.
 4. The assembly of claim 3, wherein the rows of flow guides aresuspended within the assembly between the top surface and the bottomsurface of the assembly and further coupled from one side surface to anopposite side surface of the assembly.
 5. The assembly of claim 3,further comprising a heating element coupled to each of the flow guidesand a controller with computer readable instructions stored onnon-transitory memory for: during exhaust flow, applying a first voltageto the positive electrode and the negative electrode of each of the flowguides to accumulate exhaust particulate matter in exhaust across thegap between the positive electrode and the negative electrode formed onadjacent flow guides; estimating a load on the sensor assembly based ona current generated across the positive and the negative electrodes; andresponsive to the load being higher than a threshold, applying a secondvoltage to the heating element of the sensor assembly to regenerate thesensor assembly.
 6. The assembly of claim 1, wherein each flow guidecomprises a rectangular block extending from one side surface to anopposite side surface of the assembly, and wherein the positiveelectrode and the negative electrode extend to a certain length alongopposite surfaces of the rectangular block.
 7. The assembly of claim 3,wherein each of the flow guide, the positive electrode, and the negativeelectrode protrude from the bottom surface of the assembly, and whereinthe multiple projections are coupled to the top surface of the assembly,each of the multiple projections projecting into the gap betweenadjacent flow guides.
 8. A particulate matter (PM) sensor assembly,comprising: a plurality of blocks made of an insulating material; aplurality of gaps, where adjacent blocks of the plurality of blocks areseparated by a gap of the plurality of gaps, the plurality of blocks andthe plurality of gaps arranged inside a sensor housing; a positiveelectrode and a negative electrode formed along two opposite, parallelleft and right side surfaces of each of the plurality of blocks,electrodes of opposite polarity formed on the adjacent blocks facingtowards the gap separating the adjacent blocks; and a plurality oftriangular projections inside the sensor housing aligned with theplurality of gaps, where an axis of a vertex of each of the plurality oftriangular projections and an axis of each of the plurality of blocksoverlap one another within the plurality of gaps.
 9. The PM sensorassembly of claim 8, wherein the sensor housing is coupled to an exhaustpassage such that exhaust enters the sensor housing, deflects offsurfaces of the plurality of triangular projections and flows into thegap between each of the adjacent blocks of the plurality of blocks, andwherein particulate matter in the exhaust collects across the gap inbetween the opposite electrodes of the adjacent blocks facing towardsthe gap as exhaust weaves across the plurality of blocks and exits thesensor housing.